Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
You lose your tournament/soccer game/whatever (you decide something applicable to you). You're sad about this. Who's there to comfort you? Your Ma (ま). She's a nice lady.
My favorite team lost, so I’m frustrated and heartbroken.
Breadman was badly defeated in a chess game by Anpanman.
"Where do you want to eat tonight?" "It’s your call. I lost the rock-paper-scissors."