In tetris, the act of sprinting is clearing a certain number of lines using tetrominoes in as little time as possible. Although the amount of lines can vary, the most common and widely known mode is clearing 40 lines (40L). The current world record holder for 40L sprint is u/Vince_HD on tetris site Jstris, with a time of 15.654 seconds.
People willing to clear 10k lines in sprint are crazy, but the amount of stamina needed for it is respectable to have.
Jstris is a guidline tetris website established by jezevec10 (u/jez) in 2014. Players don't have to register to play singleplayer, 1v1, or multiplayer tetris, and they can change keys, controls (like DAS and ARR) and block skins to their liking. There is also a public Jstris Discord, where people can seek help in playing and gain new friends with a common interest.
Jstris is better than tetr.io
"Stop playing 10KL sprint, that's not what Jstris is for"