LF
LF has 2 meanings
Left field
A baseball acronym that refers to left field; commonly used to indicate the defensive position of the player who is in left field; often seen in lineups and fantasy baseball.
Example
Who do you think is the greatest LF of all-time?
Def Ted Williams!
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Gamers use LF when they're "looking for" someone or something. You're most likely to encounter this acronym while playing WoW and other MMORPGs.
In MMORPGs, players often post that they're LFG or LFP when they need other players to adventure with. You may also see players post LF1M, when they need just one other player for their group.