To “tag up” is a baseball term. Consider a runner on base with fewer than two outs. The batter hits a fly ball. The runner can attempt to advance, but with a caveat. If the ball is caught, the runner must return to his original base, and if the fielder can throw it to that base before the runner gets back, the runner is out. So typically a runner will advance some distance from the base, ready to take off running if the ball is not caught, or to return to the base if it is. But once the ball is caught and the runner has touched his base, he is free to take his best shot. So if the fly ball is hit deeply, the runner may return to his base before it is caught, then take off the instant the fielder touches it. This is known as the runner “tagging up.” This is not an official term, but it is bog standard. I don’t think anyone would consider it slang.
The question arose on another forum of how old the term is, so I looked it up in Dickson’s Baseball Dictionary. I was surprised to see the first usage listed as 1935. Could it really be that late? The non-slang baseball vocabulary was well established long before then. So I did a newspaper dive. I antedated it to 1912, but this still is late. But I have a theory about its etymology that I want to run past y’all here, as a sanity check.
While I don’t find the modern sense before 1912, to “tag up” appears quite frequently around the turn of the century. It is used as a transitive verb, apparently meaning to post, as on a bulletin board. In the baseball context it often meant to score a run. The image, presumably, is that the run is tagged up, i.e. posted, on the scoreboard. Here is an example from the Honolulu Advertiser of August 14, 1902:
Cunha tagged up one in the fourth on his own double and Joy’s triple…
Here is the earliest example I have of the modern sense, from the Greenville (S.C.) News of July 14, 1912:
With the bases full, Gosham hit a long fly to Yount, Wilbur tagging up and scoring.
Here the event of “tagging up” clearly is distinct from the resulting score. How did this shift occur? A runner can tag up and attempt to advance from any base, but the most common situation by far in which he does this is on a deep fly ball is when that runner is at third base. This is both because he is running away from the outfielder making the catch, who therefore has a long distance to throw; and because the payoff of scoring is higher than merely advancing a base, making the risk worthwhile. Tagging up at second base to advance to third is much less common, and tagging up a first base is essentially unknown unless there is some other runner who draws the throw from the outfielder. So a runner at third tagging up a run on a deep fly ball was reinterpreted as the runner tagging up his base, then scoring.
The usage seems to have caught on pretty quickly. Here it is extended to a runner from second. This is from the Columbus (Ga.) Daily Enquirer of April 18, 1913. Moore is at third base and McClain at second. The batter hits a fly ball to Matthieu:
Matthieu settled under it, and Moore, after tagging up, went over the pan. The crowd yelled, but instead of throwing home, to catch Moore, Matthieu used his head and threw to third, catching McClain, who had also tagged up on the fly, completing a double play.
It may or may not be significant that both of these early uses are from Southern papers. This will require more digging. In the meantime, what do y’all think? Plausible? Insane? Banally obvious?