In looking at the picture on the Spring Wrap-up on QB's, I noticed that every one of our QB's wear a knee brace on their left knee.  With all being right-handed QB's, this obviously leads you to believe our QB's are wearing braces on their "lead throwing leg."    Any medical logic as to why?  Is it about protecting from hyper-extension from low hit or something else?

As I do some quick searches, many - but far from all - NFL and College QB's wear similar braces on their front leg.