A little excessive for a 4 year old but not felony worthy. I remember getting hit with a switch plenty hard enough to leave marks but didn't think anything of it
On a 4 year old, that's definitely excessive because 4 year old doesn't really have a very good understanding of consequences and what really defines bad behavior.
I'm all for disciplining a 4 year old, that's how they learn. But, you don't need to whip the shit out of him.