If you pull that out, the air will come out of the ball.
You'll let the air out if you take that off.
この場合、次のような言い方ができますよ。
ーIf you pull that out, the air will come out of the ball.
「それ引っ張ったら、ボールの空気が抜けちゃうよ」
ーYou'll let the air out if you take that off.
「それ引っ張ったら空気抜けちゃうよ」
ご参考まで!