From TF2 Wiki
Saw blades are an environmental hazard unique to the map Sawmill, though they also appear in some custom maps. They run in set grooves along either side of the capture point in the center of the map. They move slowly enough that players can move out of the way, but fast enough to catch sluggish or distracted players unaware, especially when they battle around the central control point.
If a player is hit by a saw blade, they will automatically be killed, regardless of other effects including being ÜberCharged or using the Dead Ringer. If a player is near death and subsequently hit by a saw blade, they will receive one death point and the player/s who damaged him will receive a "finished off" kill.
- There are basketball hoops on the wall to either side of each saw blade in order to catch launched ragdolls.
- There is a glitch where the saw blades may become invisible until they hit a player.
- A legitimate strategy is to knock your opponent into the saw blades using the Force-A-Nature or the Flamethrower's compression blast.
- After a player dies on a saw blade, the player's blood will stain the blade until the next round.