I do not believe we want a specific definition. I like @maven's words on this and agree. There are some things that having a specific definition on starts to tie our hands rather than free up our judgment.
I would bring focus to the bolded line above though. While I wouldn't consider that malicious contact in and of itself, I think it definitely lends itself to helping make your case. This is an illegal action that is being done deliberately. It is an action that intends to use illegal force to attain a desired outcome. The intent may not be to injure, but the intent is to use illegal force.
The size discrepancy, as you note, may be the deciding factor. As you said, a similarly sized catcher may have had a different outcome and negated the MC factor, even though the action was still the same. The specific action was intended either way, but doing so in one case is wantonly reckless.
From this, I think your MC was a justified call.