I made a little video explaining how to end it Wrist Slap, How to stop it when shooting a bow - YouTube
Happens to a lot of people who have a draw length set to long. I always cringe watching people draw a bow without an arrow nocked. Don't like seeing that in videos. Otherwise nicely done!
I shoot with a t-shirt on and no arm guard all summer. I only wear an arm guard during hunting to keep my jacket from getting clipped by the string.