strike one =?

A term from the game of baseball.

Somebody will come along soon to explain it better than I can. I think it's an unplayable pitch (foul throw), of which the pitcher is allowed three.

So, this is a kind of "first warning". I think.

McT has it somewhat confused. It does come from baseball. The pitcher throws to the catcher, and attempts to put the batter out. If the ball crosses the plate (a five-sided "base" behind which the catcher crouches) within a certain narrow range, it is a strike. If the ball is outside the range, it is a ball. Three strikes, and the batter is out, and a new batter come to the plate. If there are four balls, the batter advances to first base. If the batter swings at the ball, and misses, that is also a strike. If the batter hits the ball within the two foul lines which stretch out at 90 degrees from one another on either side of the plate, the ball is in play and the batter runs toward first base, attempting to reach first base before the ball is thrown there.

A very common expression arising from this is "three strikes and you're out." It is used figuratively. In this case, the use of "that's strike one" means that you've got three chances, and you've just wasted one of them. McT's use of "first warning" is reasonably descriptive.

Yes, it means:

You've had your first of three warnings.

Thank you all.