There are a number of different running back categories in football. They typically have different playstyles, strengths, and weaknesses that can be utilized by an offense in a particular formation or play type. Those types of running backs are:
The halfback, also called tailback, is the classic running back. That is, he lines up a few yards behind the quarterback, and his main duty is to run with the ball in running plays. The halfback can also help in passing plays by blocking or even by receiving a pass sometimes. Halfbacks are fast runners and agile players that can escape tackles and leave defensive players behind. The halfback is the most glamorous of the running back positions as he is the one carrying the ball most of the time.
When teams use offensive formations with two running backs, it is usually one halfback and one fullback. The fullback will position himself between the quarterback and the halfback, and his job is to protect the halfback and open the way for him to run. The blocking duties make it necessary that fullbacks are bigger and stronger than halfbacks, which is important since they will be facing very strong defensive linemen.
The fullback, similar to the halfback, can also carry the ball and receive passes if the coach wants him to do so in a play. As the game is evolving, the fullback position is becoming more unusual, with many teams not having players that specifically play the position. In that case, when needed players with similar body types such as tight ends can play the fullback position.
The wingback is the most versatile of the running back positions. The wingback is positioned one yard back from the line of scrimmage, near the tight end. There is no true common duty for wingbacks; their job will vary according to the play and can vary between handoffs, running, receiving, and passes. All those movement possibilities can make the defense confused, and facilitate a play or a touchdown. There are no players whose specific position is wingback; different athletes with different skills and body types can play the position depending on what is needed on each play.
Though the above list encompasses the position names and jobs associated with particular types of running backs, there are a number of other names given to running backs to describe their traits and where they excel in particular. Those are as follows:
A power back is a big strong running back who uses all his power and strength to get past defenders and run with the ball. Power backs are not very fast or agile due to their size and weight; their main goal is not to have long runs, but to get those crucial yards in a third down situation or maybe the remaining yards on a touchdown drive.
The speed back can be considered to be the opposite of the power back. Speed backs are fast and agile and use those abilities to get past defenders. Coaches draw plays for speed backs where they can run long runs, and those types of players are used at the beginning of a down cycle. Speed backs do not have the muscle that power backs have, and so they will be easily stopped by defensive linemen.
All purpose backs are an extremely valuable type of player. These individuals can do it all; they have a rare combination of skill and strength that allows them to perform well in many plays. A good all purpose back can change a whole team, as their versatility and abilities will have an impact on the whole offensive system and the way it executes plays.
A blocking back is the type of running back that plays the fullback position most of the time. Their main job is to block, protect the ball carrier, and open space to other runners. They are big and strong players with a tough mindset. Blocking backs can also run with the ball, but their main job is to block.