original tag map, help please

[NightFantom]

i've been thinking about an original tf2 map, somehow (don't ask) i got the idea of a new gamestyle instead of a new map
everyone knows payload, control points, and it goes on and on, but there are also non-valve created game types like dodgeball
so somehow i got the idea of playing a game of tag

base mechanics would be that one player is on RED and the others are all on BLU
the RED guy needs to kill someone from the other team and they switch teams, with the 'loser' on RED and the winner running for his life again

the problem is, i've got no idea how to do things like this, can they be done in hammer? if so how?
also there will be a few pitfalls i/we'll have to avoid, like what if the RED guy quits or goes spectator? (can this be done by auto-balancing?)
should BLU be able to attack? if they can, they could spawncamp the RED guy, but if they can't attack the scout would be unstoppable

also i wanted to ask what maps you guys would think would be fitted for a game of tag

[Haymakers9th]

majority team can't damage, everyone is scoot? that's just the sudden "should they be able to damage" point I'm not smart enough to do mapmaking shit

[NightFantom]

everyone going the same class would be an option i guess