Because of the gravitational influence of the hammer, he can't let the hammer get anywhere close to him, or the gravitational field will slow him down, which will make the hammer catch up to him and crush him. This means he can't dodge the hammer by a few inches. He has to run around to give the hammer a wide berth.
She had gone some distance when she saw this outcome. The turn of events pleased her, and she decided to capitalize on his inability to deal with her by turning back to fight him.
As it appeared, this was a good decision because the hammer had finally gotten close to the swordsman. The increase in gravity weighed the swordsman down and slowed him down even more. This effect only increased the closer the hammer got to him.
So as the hammer got to him, the slower and heavier he became. Eventually, he became unable to move and was struck head-on by the hammer.
