Wow. These multi-accounters are really innovative.

There is little depth to attacking and defending gyms. Attacking is just tap (and dodge if you want), and defending is just GRB spamming and optimising defenders to extend battle time and minimise usage of GRBs.
So, one of our local multi-accounters has "invented" a new trick to delay attackers, making use of the network error glitch.
This guy has previously discovered several tricks on his own, such as the sync attack (before it was posted on reddit); as well as taking out a defender at the back of the gym while only reducing the defender(s) in front by 1 motivation round.

Basically, when his gym gets attacked, he attacks the gym with an alt account of a different colour, which had done the last raid at the gym, and attacks the first defender. This causes all attackers to also get the same error and makes the first defender undefeatable, so attackers cannot continue attacking. He continues this until the attacker gives up.