I'm still a bit fuzzy on when certain things can be done, and I have heard conflicting answers. Suppose I attack with two creatures. I'll say that I am attacking as I tap and slide the creatures towards my opponent. He then says he is tapping them with Send to Sleep. From my point of view, they are already tapped. From his point of view he is tapping them before I tapped them. I think this is where priority and the stack come in. What is the actual sequence of events and can he do it?
For your opponent to tap your creatures, he would have to do so during your beginning of combat step at the latest. Players don’t receive priority in the declare attackers step until after attackers have been declared. That said, if you rush from your main phase to that point, we can rewind the game to give your opponent a chance to act before you declare attackers.
Your opponent doesn’t get to respond and tap your creatures after you’ve declared which creatures you’re attacking with. Your opponent would have to cast Send to Sleep in your beginning of combat step before they know which creatures you intend to attack with.