was this the correct call?

Ball remains live.

When this happens and the runner takes off for first base I say loudly: "batter is out". This usually prevents any confusion. If the B/R continues to run and the catcher throws the ball away, play continues.

The defense is responsible for knowing the situation. In this case that the B/R can't legally advance.

2 things here. The catcher did not know the rule and neither did the umpire. It is amazing. I work clinics still and one of the things I do is go over certain rules. 3 in particular dropped third strike, infield fly, and catchers interference. I am surprised at some of the answers I get especially from high school kids.

is that CAN"T advance or advance at your own risk?

not forced to advance. but they can advance at own risk. example 0 or 1 out ball in dirt batter swings for strike three ball gets by catcher batter is out but the runners can advance. now with 2 outs all bets are off

I used to say "batter's out" when the B/R can't advance on a DTS but I don't anymore. The players are supposed to know the rules. IMO, telling them the rule in the middle of a play is coaching. I will announce "no catch" and signal safe when the DTS is relevant, and the catcher and batter need to know my call (i.e., when the B/R can advance), but otherwise I just signal the swinging strike and say nothing.

A friend of mine (ahem) once called "batter's out" with the bases juiced and 2 out, and everybody stopped. If you never call it, you will never F it up.

Back when I used to call a lot more youth ball, I too, used to announce "batters out!! batters out!!"....and in many circles of umpiring this is called "preventive umpiring".......its meant to avoid these such issues......

that being said, like dash.....I no longer do this...it is the players responsibility (offensive and defensive) to know the situation.....

batters out, runners advance at your risk to be put out.....

thanks guy's, i knew i'd get the answer here.

Had this happen in a VARSITY game the other day. Catcher dropped third strike with runners on 1st and 2nd,with 1 out, he threw to 1st and the runners moved up. The coach came out and argued that the runners should go back....NO WAY!!!