Why does playing online change my video settings?

I've never been a huge fan of playing basketball games online due to the cheese factor, but i decided to give 2k13 a shot online
FIrst thing i noticed is that the framerate was lower and I was getting massive screen tearing. It looks like playing online forces v-sync off. I've never been able to play video games with v-sync off as the screen tearing gives me a headache.
Anyone know why online mode would force v-sync off? Or if there is some sort of fix I can do to force it on?

if you force vsync through your graphics card control panel it should stick

framerate is dependent on both players' machines and connection strength

thanks for the reply. Forced v-sync on and fired up fraps so i can bail out of low fps games now.

Still not sure why they would turn v-sync off though