Blocking Rules: Chop Blocks, Blocks in the Back and Peel-Backs

By 4Football Staff · October 15, 2026 · 11 min read

Blocking is legal contact until it comes from the wrong side or the wrong height. Here is how block-in-the-back, clipping, chop and peel-back rules work.

A punt returner catches the ball near the sideline, finds a seam and sprints for what looks like a touchdown. The crowd is on its feet. Then a yellow flag lands somewhere behind the runner, near a pile of bodies that nobody was watching, and the return is erased. The announcer says "block in the back," the replay shows a blocker shoving a defender between the shoulder blades, and the offense starts over from its own side of the field.

Blocking penalties are among the most common flags in football, and among the most argued over, because they happen away from the ball and in a split second. Yet the rules behind them follow a small number of ideas. A block is legal when it comes from the right direction, at the right height, with the right part of the body, against a player who is in the right situation. Almost every blocking foul breaks one of those four conditions.

This guide walks through the ideas first and then the specific fouls: the block in the back, clipping, the low block, the chop block, the peel-back and the crackback. Details differ between the NFL, college football (governed by the NCAA rule book) and high school football (governed by the National Federation of State High School Associations, or NFHS, rules, which each state association adopts and sometimes changes), so we say where each level diverges and where you should check the current rule book.

The four questions behind every blocking call

When an official decides whether a block was legal, the thinking usually boils down to four questions.

1. Where did the contact come from? Contact from the front or the side is generally fine. Contact from behind is restricted.
2. How high was it? Contact above the waist is the normal, safe zone. Contact at or below the waist is heavily restricted, because it targets the knees and ankles.
3. What part of the body was used? Shoulders, chest and hands inside the opponent's frame are the usual tools. Leading with the helmet, striking with a forearm to the head or neck, and grabbing or hooking are not.
4. What was the situation? The same hit can be legal in one context and illegal in another. An opponent already engaged with a teammate, a defender who has his back to the play, a player who has not yet touched the ball, or a blocker coming back toward his own goal line can all change the answer.

Keep those four questions in mind and the long list of named fouls becomes easier to hold in your head. A "block in the back" is a failure on question one. A "clip" fails question one and two together. A "chop block" is a failure on questions two and four. A "peel-back" is a failure on questions two and four from a different angle.

What a legal block looks like

Before the fouls, it helps to see the baseline. A legal block is an attempt to take a defender out of the play by contact with the blocker's body. At every level of the sport the blocker may use his shoulders, his chest and his hands, and the hands must be inside the defender's frame, meaning on the body between the shoulders rather than on the head or the face mask. The blocker may not hold, grab and restrict; that separate foul is covered in our guide to offensive and defensive holding.

The blocker may also be a defender. Defensive players block too, most often on interceptions and fumble returns, when the defense becomes the offense and the former offensive players become tacklers. Every rule in this article applies to them in the same way once the ball changes hands.

The block in the back

The block in the back is the foul in the opening scene. It is a push or hit from behind, above the waist, against an opponent who is not the ball carrier. The NFL, the NCAA and high school rules all treat it as a 10-yard penalty. The enforcement point depends on the type of play and the rulebook, so the 10 yards may be measured from the spot of the foul, the previous spot, or the end of a return; check our penalty enforcement guide for how those spots work.

Why it is called so often on returns

On kick returns, blockers frequently run alongside defenders who are racing downfield, then try to turn them. A defender who is running full speed with his back to the blocker is, almost by definition, exposed to contact from behind. The blocker has two legal options: get in front of the defender or hit him from the side. Chasing him and pushing from behind is the foul. Returns are also the place where the contact is hardest to see, because the play is stretched across the field and the flag often falls on the far side of the action from the ball.

When it is not a foul

Officials do not call a block in the back every time a hand touches a back. The common exceptions follow the same spirit as the four questions.

• The defender turns away. If a defender spins or turns his back to the blocker on his own, the blocker is not penalized for contact that follows. The foul is about the blocker's choice to attack a player who was facing away, not about a defender who hid his numbers.
• The opponent is the ball carrier. Blocking a runner from behind is not a block in the back; it is a tackle, and tackling is legal.
• The contact is below the numbers but not a push. Incidental contact while both players are running is not enough. Officials look for a push or a block, a clear attempt to take the defender out of the play.
• Close-line play near the snap. In a small area around the ball at the snap, the rules about contact from behind are more forgiving, because linemen are packed together and moving in every direction. The size and shape of that zone differs between rule books, so players and coaches should read the exact language for their level.

A good rule of thumb for a spectator is this: watch the defender's shoulders. If his numbers are facing the blocker and the blocker's hands land on them, the flag is likely. If the defender is turned sideways and the blocker's contact is on his side, it usually is not.

Clipping and the low block

Clipping is blocking an opponent from behind at or below the waist. In the NFL, college and high school rule books it is a 15-yard penalty. It is one of the oldest named fouls in the sport, and it is more serious than a block in the back because contact at the back of the knees or lower leg can injure the joint.

A low block is a block at or below the waist from the front or side that is not allowed under the rules for the situation. This is where the rule books differ most.

• High school and college rule books define a "free-blocking zone," a rectangle around the snapper that extends a few yards to each side of the ball and a few yards behind the line of scrimmage. Within that zone, linemen who started in it at the snap may block below the waist, under conditions the book spells out. Outside the zone, or by players who started elsewhere, a block below the waist is a foul.
• The NFL uses the "tackle box" idea instead. Certain offensive linemen in the box can block low in limited circumstances, but a back who was in the backfield at the snap, or a receiver in motion, generally cannot block below the waist.

The further a blocker is from the tight cluster of linemen at the snap, the more likely a low block is illegal. The penalty is typically 15 yards.

Why so strict? A block that hits the legs of a defender who is engaged high or running upfield offers little chance to protect the knee. Football's rule makers have moved the sport away from low blocks over many decades; for the broader story, see our history of safety rules in football.

The chop block

The chop block is the best-known of the named low blocks and the one most often misunderstood. In plain terms, a chop block happens when one offensive player blocks a defender high while a second offensive player blocks the same defender low, at the thigh or below. The defender is hit from two directions at different heights, and he cannot protect either level.

A slow-motion version looks like this, using a hypothetical play. A guard and a tackle double-team a defensive tackle. The guard engages him chest to chest. While the defender is locked up, the tackle dives at his knees from the side. Both players are doing something that is legal on its own, but the combination is the foul.

The key points:

• It requires two blockers (or a defender already engaged by one). A single blocker hitting a defender low is a low-block question, not a chop.
• The first contact must be high and engaging. If the defender is simply running free, a low block is judged by the low-block rules.
• The penalty is 15 yards in the NFL, college and high school football.

NFL and college rule books list a few exceptions for the opening stages of a play, such as a defender who is still standing near the line at the snap, but they are tightly written. If you are a coach or player, read the exact exception language for your level and teach your blockers to avoid even the appearance of the combination. If one blocker has the high side, the other should not go for the knees.

The peel-back and the crackback

Two more named fouls are about blockers who come back toward the play from outside it.

The peel-back block

A peel-back is a block by an offensive player who was positioned outside the main cluster of linemen (or was in motion), who then moves back toward his own end line, and makes contact at or below the waist with a defender. Think of a wide receiver or a back who lines up outside, then "peels" back inside to take out a pursuing linebacker's legs. The defender is coming across the field and cannot see the blocker approaching from behind and below. The penalty is 15 yards in the NFL and the NCAA rule book also prohibits the block. The NFL describes it specifically; other rule books fold it into their low-block rules.

The crackback block

A crackback is the term for a receiver or back lined up wide who comes back toward the ball and blocks a defender who has been going the other way. Many crackback blocks are perfectly legal: a receiver who hits a linebacker in the chest or shoulder is doing his job. The illegal versions are those that are low, those that are to the head or neck area, or those that approach the defender from the side or back in the wrong zone. The NFL penalizes illegal crackbacks at 15 yards; college and high school rule books contain similar prohibitions.

Blocking on kicks and returns

Because blocks happen in open space on kicks, the special teams rule sets are the most detailed. A few themes:

• Blind-side blocks by a player running toward his own end line against a defender who cannot see him are restricted, especially with the helmet or forearm.
• Fair-catch protection: players may not block a receiver who has signaled for a fair catch. That is a separate foul with its own penalty, but it often shows up in the same flurry of flags.

Quick comparison by level

The yardage is the same in most cases, so the real difference is the definition: where a low block is allowed, who is allowed to make it, and what zone counts as "close-line play." A coach moving a player from one level to another should not assume the definitions carry over. If you coach in a youth or recreational league, the rule set may be a modified version of the high school rules; ask your league office for its current wording.

How officials see it, and what you can do as a fan

On a typical play, different members of the crew watch different areas. The officials near the line watch the blocks on the line itself, while the officials downfield watch blocks away from the ball. Our guide to the seven on-field officials explains who watches what and why a flag sometimes comes from a different part of the field than you expected.

As a viewer, a few habits help you anticipate a flag:

• Watch the defender's numbers. If he is facing away from the blocker when contact starts, think block in the back.
• Watch the knees. If a blocker's body is dropping or diving toward the defender's lower legs, think clip, low block or chop.
• Watch for two blockers on one defender. If one is high and one is low, think chop.
• Watch the wide player who returns inside. If he hits low as he comes back, think peel-back.

If you want to see the penalties called in context, the live scores page links to the games as they are played, and the Play section is a good starting point if you are a recreational player who wants to learn how a legal block looks before you ever run into a flag.

How coaches teach legal blocking

A well-coached team spends time on blocking technique, partly to win and partly to avoid these flags. The usual points are consistent from level to level: keep your eyes up and your hands inside, run through the defender instead of around him, keep your feet moving, and when the defender turns away, release him and find another target. Our guide to blocking fundamentals goes through stance, hands and leverage in detail.

For high school coaches and players, the most important practical advice is to learn the specific rule for your state. State associations adopt the NFHS rule book but can make changes, and a few of them modify blocking rules. Your association's website or your athletic director is the right place to confirm. Our high school directory can help you find your state association's page and your local schools.

The short version

• Blocking is legal contact if it comes from the front or side, above the waist, with the shoulders, chest or hands inside the frame.
• A block in the back is contact from behind above the waist on a player who is not the ball carrier: 10 yards.
• Clipping is contact from behind at or below the waist: 15 yards.
• A chop block combines a high block and a low block on the same defender: 15 yards.
• Peel-back and illegal crackback blocks involve a blocker coming back toward his own end line or the ball and hitting low or to the head and neck: 15 yards.
• Definitions of where a low block is allowed vary between the NFL, college and high school rule books, so always read the rule for your level.
• When a defender turns his back to a blocker on his own, a block in the back is usually not called.