Divide the class into 2 teams they line up side by side in 2 lines. Choose 3 bases (sets of desks, corners, etc).
Team A bats...I hold up a flashcard and the person at bat (first one in line) has 5 seconds to say the correct answer. If they get it right they go to first base. Team B is mouthing wrong answers to try and trip up the batter. Play coninues like this until Team A gets 3 outs or 5 runs. Then it switches and Team B bats. Every once and a while I'll throw in a double or triple flashcard.
My kids also really love arond the world... anything to make math more fun