[throw in] vt (1678) 1: to add as a gratuity or supplement
2: to introduce or interject in the course of something: contribute "they throw in some ... sound effects on several songs --Tom Phillips"
3: distribute 3b
4: engage "throw in the clutch" ~ vi: to enter into association or partnership: join "agrees to throw in with a crooked ex-cop --Newsweek" -- throw in the towel also throw in the sponge : to abandon a struggle or contest: acknowledge defeat: give up