(third-person singular simple present tags up, present participle tagging up, simple past and past participle tagged up)
(baseball) Of a baserunner, when a fly ball is hit, to put one's foot on the base one is currently at until the ball is caught. When the ball is caught, the baserunner may attempt to advance to the next base, at the risk of being tagged out.
English Wiktionary. Available under CC-BY-SA license.