Oven spring is the very fast initial rise from hitting the stone, as the gases (steam and CO2) get heated and expand.
Your crust looks quite flat to me, whereas i tend to imagine neapolitan pizza's are bubbly at the rim, and thin in the middle. It could be as a consequence of the shaping, i leave a rim of dough at the edge of mine to achieve the thicker bubbly rim.
I don't really know why your pie has not risen properly. I use starter only now, rather than bought yeast, but i would think that active yeast should provide plenty of spring. Maybe you need to have a period of proofing at room temp before retarding in the fridge, or just have a longer fermentation in total.
Another factor is oven temperature, how hot is your oven?