How do you 'hit the rudder blade' with your foot while sailing? Did he fall overboard and get run over?

My kid did that once on my Hobie 18 on a fast reach, missed his trap hook and fell off. The rudder blade hit is thigh so hard I was sure it was broken, but it wasn't, just left a hell of a bruise (on his thigh, not the rudder!).

His mother was not impressed to say the least!