Yes, tag is a Scrabble word!

Verb

1. Attach a tag or label to

2. Touch a player while he is holding the ball

3. Provide with a name or nickname

4. Go after with the intent to catch

5. Supply (blank verse or prose) with rhymes

Noun

1. A label written or printed on paper, cardboard, or plastic that is attached to something to indicate its owner, nature, price, etc.

2. A label associated with something for the purpose of identification

3. A small piece of cloth or paper

4. A game in which one child chases the others; the one who is caught becomes the next chaser

5. (sports) the act of touching a player in a game (which changes their status in the game)