Can this sign be used to mean 'I lost'?
No, this specific motion means to defeat or conquer someone else. If you want to say 'I lost' or 'I failed', you would use the sign for 'lose', where a 'V' handshape strikes downward onto the open palm of your other hand.
Is this the same sign used for beating someone in a game?
Yes! This sign is commonly used in the context of sports, video games, or competitions to mean 'beat', 'conquer', or 'overcome'.
Does the direction of the sign matter?
Yes, 'defeat' can act as a directional verb. The standard form shown here generally means 'to defeat someone'. If you alter the movement so the dominant hand strikes backward toward your own body, it changes the meaning to 'it defeated me' or 'I was defeated'.