QUICK ANSWER

Halfbacks and fullbacks both line up in the backfield, but halfbacks are usually the main ball carrier and rely on speed, while fullbacks are bigger and spend more of their time blocking.

The main difference between a halfback and a fullback is their job. A halfback is usually the team's main ball carrier, while a fullback is a bigger player who mostly blocks.

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Both positions can run, block, and catch passes. What changes is how often they do each one.

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Blocking

Blocking is the fullback's main job. On many run plays, he goes through the hole first and blocks the first defender he meets. The ball carrier follows behind him.

A halfback blocks too, but usually in pass protection, when he stays back to help protect the quarterback.

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Running The Ball

The halfback is the team's main runner. A lead back can get 20 or more carries in a game.

Fullbacks get far fewer carries, and many finish a game without any. When they do run, it is often on short-yardage plays.

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Catching Passes

Halfbacks also catch more passes. In many offenses, the halfback is a regular target out of the backfield.

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Fullbacks run routes too, but they usually see only a few targets, if any.

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Size And Build

Fullbacks tend to be heavier and more muscular, which helps them block linebackers.

Halfbacks are usually leaner and more agile, which helps them make defenders miss.