[Undesirable]

Here are a few suggestions:

1. If you're completely re-vamping the sniper, their rifle could be replaced with a briefcase containing a sniping kit, complete with tripod, which has to be set up before they can utilise their ultimate weapons of doom. The engineer should also be able to build sandbags or small concrete bunkers mid-map to help protect the sniper's coveted position and not limit them to the usual boring places to seek cover. However, their effective sniping field of view will be reduced to 90° - 180° until they re-mount the tripod in a different position, which would take time.

2. If you're just sticking with the normal sniper rifle, simply reduce their accuracy by introducing swaying (breathing) that is more pronounced when the sniper is standing than when he is crouched. Introduce a new prone position where the swaying is very much lessened (gotta give the snipers something to look forward to). You could also reduce their effectiveness by limiting the angle that the sniper is able to aim whilst the rifle is charging up.

3. Add proper scope effect to reduce field of view to a smaller circle.

4. Replace the autorifle with a fairly powerful silenced firearm, which can score critical hits and is more powerful the closer you are to the victim, but is ineffective at long-range.

5. Give the sniper proximity mines (or directional anti-personnel mines) in his secondary grenade slot, which can be shot or detonated by other explosions nearby, thus not rendering them overpowered.

6. Remove the tagging ability of a sniper and put it on the spy's tranq gun instead.

Edit: 7. Travel time and bullet drop (gravity effects) for sniper rounds.