I just crushed a flat tick (I was out cutting grass) and s/he was full of white goop. What was that?
It’s guts?
I’ve dispatched many, many ticks and I’ve never seen white goop. 
Eggs?
That’s not “white goop”, it’s a creamy filling of justice!
SPOON!
CMC fnord!
Frikin’ gross is what that was. Blech.
I’ve never seen a tick do that.
creamy filling of justice
Band Name!
Picture?
*loves being the person who thinks to ask… 
*
Eggs.
Alas, I didn’t have a camera with me while cutting grass.
Perhaps it wasn’t feeling well, and you disturbed it’s vomit reflex.
Probably not, as they need a blood meal to produce their eggs, and if this one was flat it hadn’t had a chance to feed. It was probably either hemolymph, some kind of innards (possibly fat deposits), or just possibly ova that had not developed much yet.
At least in my experience, a tick’s hemolymph (the arthopod equivalent of blood) is fairly clear, but I suppose in some circumstances or in certain species it could be whitish. The hemolymph does not circulate via blood vessels, but instead fills most of the arthopod’s body cavity.