Thats the thing about splitting. The one splitting can usually 1v1/2 everyone else on the map, so if you dont either group and 4v5 or stop the split pusher by getting a kill, youre in for it.
But the thing about splitpushing is that in order for it to work, the splitpushers Team NEEDS to pressure another objective or else they just get picked off.
So as long as you have stronger wave clear then the enemy team, or as long as everyone is relativley even, they wont be able to splitpush properly. You also have to telegraph how fast the splitpusher can push, and cut him off before he even reaches the vicinity of the tower, or force out a fight before he gets there, less you risk losing the turret. The rest of his team have time to clear their waves and pressure something if you let him get anywhere near the tower.