Sourdough instead of dry yeast?

I do sourdough instead of commercial yeast regularly - I'd say go with a percentage of starter to bread flour (baker's percentage) you're comfortable with and continue on with the recipe, allowing for the possible slower rise of sourdough. The recipes I use typically call for 15-20% starter by weight to the weight of flour in the final dough. For 2c of flour you shouldn't need much starter, if you were doing 20% that should be 48g. But honestly, at this point I just eyeball the starter and go from there. For this amount of flour I wouldn't do more than 1/4c, but pizza is very forgiving in my experience.