The act of sliding under a table or obstacle, usually on one's belly or all fours to reach one's goal. Often used in the context of a house rule for Beirut (what you ignorant people call "beer pong"). This rule allows one to dive under the table to retrieve a ball after they have missed a shot, thus getting a behind the back shot before their turn ends.
When used in the context of Beirut it is usually used in conjunction with the 50-yard line
It may also be used to describe an escape from a situation requiring you to go underground (literally or figuratively).
"Did you see Ted? He just Harriet Tubman'd the shit out of that ball"
"House Rules: both people sink a cup = balls back, ..., 50-yard line, no Harriet Tubman..."
"I built an igloo last week with an underground tunnel, just in case I had to Harriet Tubman that shit if we were attacked."