Maybe you've done some training before, but there's a big size difference here. There's no way you can beat me.

Maybe you've done some training before, but there's a big size difference here.
There's no way you can beat me.
たぶん君は格闘技習ったことあるかもしれないけれど体格に違いがある。
君が私に勝てるわけないでしょ。