The offence would be force, as you state. But the player has not been hurt, there is no cut, bruise, laceration, swelling or anything else that suggests this ball has been thrown at the players face with excessive force. That is unless the player has suffered internal bleeding or something, which I absolutely doubt.
There are two sides to this and I see your point in saying VC but you have to look at it from a different perspective. Players have an altercation, they have a push and a shove and nothing more, you know what I mean, the type you see in most games. Toys thrown out the prom. Now, these punches etc that you get are a lot more forceful than this ball yet the usual outcome for handbags is a stern talking to. If you are going to dismiss the keeper for excessive force, you have to be consistent in your approach and definition of the term "excessive" for the rest of the game. I can guarantee you that the game would be abandoned.