^^^I have heard this...5 sets of 30 second all out (100%) sprints with 3 and a half minute rest in between.
Problem is in softball, no one is doing that. Inside the park HR should take no more then 20 seconds and that is not "all out" (slowing up around the bases, slowing up at home, stopping because someone dropped the ball, etc.) and even then one would need 5 of those in a game while not having the extended rest periods.
Agree with Kangaroo 300 calories/game max and even then I'd guess that would be in the OF with two others, chasing lots of hits in the gap and then having the same situation when it is time for you to hit.
I think that might be about right for an average. Obviously catchers and corner IFers probably run the least with OFers running the most.
It's all relative, but you jog in and out, sprint on the bases if you get a hit, sprint for balls in the outfield, etc. As a pitcher, I backpedal pretty hard 2-3 steps every pitch, have to sprint as hard as I can to cover first at least 3 times a game, and presumably have to run the bases at least 2 since I bat last.
IF 4 full out sprints is more than 45 seconds of steady cardio I don't think that 400 is too high of an estimate. The hardest part of softball to me, is the changing of directions, and that's got to be harder than a sprint takeoff when you're slowing and starting back in the opposite direction.