slip in

verb

1. To include (e.g. a certain word or phrase) into a sentence discreetly
2. To enter discreetly.

   “The visitors we do not encourage are the many small boys who slip in unobserved and are a danger to themselves and the staff.”

3. To play a subtle pass into someone in a goalscoring position.

   “A minute into the second half, Hazard blasted the second goal right over Gordon's head and into his net. Soon after, Charlie Mulgrew's aimless ball out of defence fell to Dembele, who gave it to Hazard. The attacker slipped in Batshuayi in for the third.”