Backup
Reserve, Spare, Copy, Stub
noun
If you abstain from doing things a lot you'll need a backup plan to get you out of things. Someone invites you to the beach? You need a backup. (It's that you are afraid of the sun, say that!)
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You learned this reading already! Good for you!
控えの選手には誰がいたっけ？
Who’s the reserve player?