Here is the full list of all 13 Lethal League achievements worth 1,000 gamerscore.
Bunt the ball at 1000 speed or above
Reach level 11
Reach a ball speed of one thousand
Hit three players in a row
Rally the ball back and forth for at least ten times
Get hit by your own ball
Reach a ball speed of one million
Reach level 22
Reach level 33
Beat the challenge mode
Beat the challenge mode without using any continues
Beat the challenge mode with every character
Play a hundred matches