if he starts to charge, turn side ways with ur elbow stickin in his direction, and once u guys actually "clash" drive forward and swing ur elbow into his stomach/chest. that'll probably know the wind outa him, from there do whatever. depending on how he fights that may or may not work. the first move in half the fights i see is one dude tacklin another...if thats the case, this will probably help. if hes comin at u at u bent...u may be able to elbow him in the face
if its a straight fist fight from the getgo, bend your legs til the point you r a lil taller than him (u said u were taller, but idk how much taller). make sure he doesnt go for an uppercut to the jaw, cuz u have to go for one. and since your legs are already bent, you will have more force behind it....if u r MUCH taller than him...elbow him on top of the head? lol