So, one of my players posted a meme about a fighter that is low health. So the fighter runs past the cleric, and the cleric says that they have warcaster and use their attack on opportunity to cast cure wounds on the fighter.

Now I have looked through all the rules and I don't see why this wouldn't work. What say you dnd community?

Edit: So this is what I have decided in my game. If you have warcaster, you may cast healing/support spells. However, you can't cast spells that require a spell component that costs money. My reasoning on this is so: say i throw a baseball at you and you're not expecting it, you wouldn't be able to put on a glove before catching it. This is what I'm doing only in my game.

As always it up to dm.