This signal is used by the Referee to indicate that an illegal block below the waist has occurred. Whilst blocking below the waist (other than from behind) is permitted in most situations, there are times when it is illegal - eg after an interception or following a kick.
PenaltyThis attracts a 15 yard penalty, usually from the spot of the foul.
This is preceded by the Personal Foul signal (S38). Begin the signal standing upright with both arms to your sides, and then raise both simultaneously by a couple of feet and give a gentle chopping motion towards your thighs, bending forwards slightly as you do so.
Finally point to the offending team by streching an arm out from the shoulder to the horizontal.