Part of a pro set called Uniformed Unicorn in which you have all like cards in a formation that can't be stolen.
Unnecessary Roughness
Flipping over a table, causing destruction to the perimeter, or fighting players. Tossing cards around. There is no actual penalty for this, but you can create a house rule.
Unsportsmanlike Conduct
Acting a fool in any manner because you lost or being a sore loser. There is no actual penalty for this, but you can create a house rule.
Upper Hand (The)
An advantage that happens in capture the flag when an opponent is in control of the flag and get an extra turn each round.