This signal is used by the Referee to indicate the personal foul of tripping has occured. It should be noted that the runner may be legally tripped.
Penalty15 yard penalty and an automatic First Down if against the defense.
The foul will preceded by the personal foul signal (S38). Begin the signal standing upright with both feet together, and then bring one foot back and behind the other to simulate a trip in an unhurried manner (vital if you don't want to fall over!).
Finally point to the offending team by stretching an arm out from the shoulder to the horizontal.