He's making her slap her thigh.

[FiveFrameSwing]

 

[FiveFrameSwing]

 

[BoardMember]

All of my pitchers learn to glove slap as a matter of course when doing drills from the nine and twelve position as we work on adduction, core contraction and fast twitch muscle training. Most continue to utilize the reciprocal value of bringing the glove hand/arm down with authority during the ballistic action of Fastpitch. A Few do not. Very few. I don't advocate for or against it past the training/drill stages. It is a style thing, not an absolute either way.