George Nipping is one of the witnesses for the defense. He is specifically called to defend James King (remember, even though Steve and King are being tried together, their fates will be decided separately of one another and their defense lawyers are working separately too – and sometimes against one another).
During his testimony, George Nipping claims that he once sold King a baseball glove that was for a left-handed person. Steve asks Petrocelli what that testimony is all about and she explains that, since the gunshot wound was on the left side of the body, Briggs is trying to make the defense that it couldn't have been done by the left-handed James King. She adds that it is not a very strong defense.
Petrocelli cross-examines him and, unsurprisingly, knocks down his argument by saying that, having never seen King shoot a gun, Nipping couldn't know how he would do it.