This is a gay term when a gay top inserts his hard penis into the bottom's ass as deep as it can go and holds it there while the bottom jerks him off using his butt muscles.
Saddlebacking - the term for the phenomenon of Christian teens engaging in unprotected anal sex in order to preserve their virginities. Named after Saddleback Church, home of the Reverend Rick Warren, who is a proponent of abstinence education, the "sex ed" that has convinced so many Christian girls and boys that buttfucking isn't actually sex. Specifically from the Mormon community.
Kristine is still a virgin in the eye's of God because the Utah Saddlebackers entered in the back door.