Jo is a little bit of a thing at just 5'3". Small and wiry, boxing is the very LAST style she should be practicing, so WHY did I do it?
1) Richard wanted her to do something outside of her comfort zone. It's not like she has much of one to begin with, but he wanted her to be CHALLENGED.
2) She needed to learn to take a hit. That's a huge thing about boxing - yeah, it teaches how to get out of the way, how to move, how to assess the situation and attack... but a bigger thing? How to take a freaking hit.
3) A little part of him wanted her to give up. He knew she wouldn't, but he really, REALLY wanted her to just throw in the towel...