The infinite should be easy enough to detect. One backthrow, that's OK. If you step forward and do another one (which you pretty much have to knowingly do instead of using a guaranteed launcher) then hit 'em with the banhammer. There's really no reason to do more than one backthrow unless it's "I'm going to infinite the other guy", as those backthrows do pitiful damage compared to the full combo you get. That's pretty simple.
To be honest, even with the infinite in play, Partisan could possibly have managed to pull through if it were Best of 5 instead of Best of 3. Just sayin'.