Virtua Tennis 4

You will get this achievement naturally as to hit atleast 124.3mph you need to produce a max serve.

You could either do this in an exhibition match as one of the world class players or just do it as you go through the world tour.

But

I produced max serves with my character a few times at the start of the world tour but maybe your starting character isnt strong enough but afer a few games my character produced a max serve to get the achievement so assuming he got stronger after those few games to produce that speed.