Banning with spells. I am just thinking of these, they are not guaranteed to work. Some of these are old and used, but I am going through every spell I can think of and find a way to use it.
Make the player unit constantly moving. Make a trigger to detect if the unit has stopped. Lockdown, stasis field, or maelstrom.
Make a unit with low HP and high sheilds and have a computer player constantly attacking it. Make it so every second or two it regains its shields. When you use EMP Shockwave it will lower its shields to 0 allowing the unit to die. (Would need large areas so you don't ban the wrong player(s), and might use it as it resets so it takes 2 uses to get it done)
Psi storm or Irradiate a unit with low HP. (Has to be spaced slightly so you don't ban other people)
Make a computer player that does not have vision with the people who are being banned, but has vision with the banner. Banner has vision with the players to be banned. The units to ban with are cloaked. Use Parasite so the computer can see and kill them.
Spawn broodlings on the units and make a trigger to remove broodlings with hypertriggers for a cool "dies from a green cloud" effect. (I used a similar thing with computer AI to start a round in a defence)
Make units constantly moving to avoid lurker attacks. Ensnare will slow them down allowing them to not outrun the attack.
Move a 1x1 location on P12 Dark Swarm or Disruption Web and remove/kill it, and the bannable player's unit. Or you can make a computer player attack the banner and Dark Swarm or Disruption Web will disable the unit to die, banning them.
Use a terran building with low HP (such as 2) and plague it. Or use any others that are actually on-topic in here.
Make a unit owned by the banner to represent each player in the game. Consume one and it bans that player.
Make a computer to blind all bannable units. If you use Restoration they will kill a computer that was normally hiddin, and 1 kill of that unit bans them.
Mind control a unit will remove it for the banner and ban them.
Feedback a unit and when it dies they are banned.
Do the reverse of the restoration.
Use optical flare to disable them of attacking a unit, banning them if they don't kill it.
Put a location for every player labelled somehow with a civilian or something. Merge two templar to form an Archon and kill the civilian, morph a lurker and detect if it exists, morph a larva that has been moved there to something, etc.
Anything else?
EDIT: "Psi or Irradiate storm" hehe.. added "Irradiate" to that one after psi storm..