That is a good question! I don't know if the program takes unit speed into account to determine who 'wins' in the case of multiple attacks against the same target, or if the attacker and target are locked in when the app writes the custom JSON to the blockchain, and thus uninterruptible.

Apparently, all it takes is for your opponent to lose a battle before yours would begin, and that will put their shields up. My instincts tell me this could mean a bunch of Ninjas sent at the same time as somebody else sending a bunch of Bouncers will win the speed war, but the Help file isn't totally clear on how this works.