A scrummage, commonly known simply as a scrum, is a method of restarting play in rugby football that involves players packing closely together with their heads down and attempting to gain possession of the ball. Depending on whether it is in rugby union or rugby league, the scrum is used either after an accidental infringement or when the ball has gone out of play. Scrums occur more often, and are now of greater importance, in union than in league. Starting play from the line of scrimmage in gridiron football is derived from the scrum.

In both forms of rugby, a scrum is formed by the players who are designated forwards binding together in three rows. The scrum then 'engages' with the opposition team so that the players' heads are interlocked with those of the other side's front row. In rugby union the initiation of the process is verbally coordinated by the referee who calls 'crouch, bind, set' as of 2013 (formerly 'crouch, touch, pause, engage', 'crouch and hold, engage' before 2007). The scrum-half from the team that did not infringe then throws the ball into the tunnel created in the space between the two sets of front rowers' legs. Both teams may then try to compete for the ball by trying to hook the ball backwards with their feet.

A key difference between the two sports is that in rugby union both sets of forwards try to push the opposition backwards while competing for the ball and thus the team that did not throw the ball into the scrum has some minimal chance of winning the possession. In practice, however, the team with the 'put-in' usually keeps possession (92% of the time with the feed) and put-ins are not straight. Forwards in rugby league do not usually push in the scrum, scrum-halves often feed the ball directly under the legs of their own front row rather than into the tunnel, and the team with the put-in usually retains possession (thereby making the 40/20 rule workable).