We'll call it a draw

The worms writhe everywhere. Shirou is distracted by the attack on Rin and a poor magus to boot, but Caster is neither. While this isn't the battlefield she would have chosen, she is still a Servant and more than a match for any mortal magician. She senses the tiny bits of magical energy that each of the worms carried within it, somehow connecting them to the enemy Master before them. They are exactly the wrong kind of thing to attack someone like her with, though she could see how someone might think they would work against Shirou. She would crush this impertinent worm for daring to....

The worms aren't attacking directly. At least, not all of them were. She spins a net around her master made of sinister rattling chains, but others are moving in strangely-coordinated fashion around.. too late, she realizes that they were forming a magical circle out of their own bodies. She speaks an incantation out of desperation, and a rippling wave of energy passes over the park. In its wake, every living thing the size of a bird and smaller is left utterly transfigured into stone. But it is too late. The worm-crafted circle blazes with a sickly green light of its own, and something reaches into her chest and tears a massive chunk out of her prana reserves. Already low due to her incomplete connection with Shirou, she staggers.

Shinji snickers as he withdraws, Rin and Rider pinned down by Archer's unrelenting barrage while Shirou has his own problems to deal with.

Shirou turns from the battlefield and finds himself face to face with an unmasked Caster. Literally, as her blazing eyes are less than an inch away from his own. Her features speak of an uncontrollable hunger, and he's literally frozen in place as she pounces.