Deliberately handles the ball is the foul. And I'm not just arguing semantics here - in cases like this, it's actually important that referees understand this - because not enough do.
The problem is, there's 'deliberate' in the meaning of his law, which doesn't really match up with the 'street' meaning of 'deliberate'. When a player sees an opponent make a clearly intentional handling of the ball, they think it's a caution for 'deliberate handling'. I'm talking slapping the ball away, or catching it in these scenarios, or jumping up to stop the ball going too far away from the field not realising they're still on the field. Players will scream these are cautions but really, the fact that it's a clearly intentional act is barely relevant.
It's only cautionable if it's done to deny an opponent possession, or done to score a goal. That's it. No other scenario. So, unless this case was, breaking up an attack (and you'd probably take any potential confusion into consideration here as well) there's no reason to caution here.
It's a mandatory caution.
There's not even a debate to it
Really? What gives you that idea? Read the Additional Advice carefully then get back to us
Personally, I'd love to hear from the other 3 people who voted 'caution' here. Because, unless there's missing critical information here, it's definitely not a caution.
From what was described, applying law 18 sounds the way to go.
I'm going to be really pedantic here - IMO Law 18 doesn't even come into it here. Law 12 answers this one quite clearly.
Law 18 may come into it if there's contention over whether it's denying an opponent possession or not, but assuming that wasn't the case (and we can only assume such from the information provided), Law 12 and the Additional Advice answer this one.