First question. what rules are you sparring with?
In general there are 2 choices for the opponent who charges. a) meet force with force such as a hard defensive side kick to make him think twice. Or b) move off line and strike. If you do EPAK think Intercepting the Ram and Charging Ram.
As a MMA aside I watched a late night MMA fight several years ago where one guy "lost" a fight by doing Intercepting the Ram. The opponent tried to shoot low and the guy did a Knee groin, hammerfist kidney and dropped the grappler into a writhing ball on the floor. Apparently the groin shot/kidney strike was illegal and the "winner was carried out and the "loser" walked away.
Jeff