Green’s Dictionary of Slang

(US gambling) a bet that it is hoped will recoup earlier losses.

1950		‘Josephine Tey’ To Love and Be Wise 216: ‘No bets on the field?’ ‘N-o. I think not. A saver on Weekley, perhaps’.
1981		D. Jenkins Baja Oklahoma 222: ‘I like the Over on Arkansas-Rice. I’m teasing the Aggies with Alabama and Army. Oregon’s the West Coast saver’.