Follow what Noyade said, and if they continue to be an asshat (yes it was me, I enjoy calling people that) then give them a kick. We can't have a general rule against it because some people do it in the beginning of the match to motivate people. It would be a problem if friendly fire was on, but since it isn't, the ones who pester people will be dealt with accordingly.
Most of the time there will be an admin of some type on the server. If he/she is active (not afk) he/she will take care of the problem. If none are present, in the future, please get the steam ids of the perpetrators and post them in the request ban forum.
honestly i think noyade said it the best. if i see someone doing that to someone else i'd ask the victim what type of punishment they would like the "asshat" to get. i think thats fair as long as its not a ban (unless they keep doing it after being told to stop).
He means when people stand in front of you and block your vision/movement of an area. For example, you are sniping, and your idiot teammate stands in front fo you and punches you until you both die. It's immature and stupid.