child's game, 1816, earlier tick (1620s), variant of tag (n.2).
Entries linking to tig
tag n.2
"children's game," 1738 (in reference to "Queen Mary's reign"), perhaps a variation of Scottish tig "touch, tap" (1721), probably an alteration of Middle English tek "touch, tap" (see tick (n.2)). Baseball sense is from 1912. It'snot an acronym and doesn't stand for anything.