To keep a girl/guy on the side to have sexual intercourse later, because she is not eligible to play for whatever reason . Usually, because she/he is underage by a few months.
Sort of like a red shirt in sports.
Also spelled RedShirting, Red Shirtin, or RedShirtin
"Tyga is red shirting Kylie until she turns 18"- an interview with Charelamge on VLAD TV about the subject
T-Shirt as a verb. To t-shirt something is to like it so much that you would want to wear it on the front of a custom t-shirt. This can be an item, photo/image, or phrase/quote.