Played a mod of ET last year and there was leaning left and right. Out of curiosity, when was this introduced?
Leaning in Wolf:ET
2003 with the game’s release.
If you are talking about the thirdperson animation of players leaning then this was introduced first in NoQuarter and later introduced in ET: Legacy as well.
The reason being that players leaning from behind a corner are seeing things that are behind that corner, yet players that are behind said corner don’t see the player, which is the literal definition of a wallhack. Therefore, thirdperson leaning animation has been introduced.
@KeMoN is correct. The leaning function in Wolf ET was taken from Rtcw, thus both SP and MP modes of the game allow a player to lean without the foes seeing them. However, at least in SP mode, the player can still take damage if bullets/projectiles are being fired while the player leans.