According to Grover who was after Percy?

Much to Percy's astonishment, his best friend Grover reveals himself as his protector. Percy had always been the one protecting Grover, getting into fights to keep the bullies away from him. But now Grover tells him that he's there to protect Percy. Percy wants to know exactly what he's protecting him from, but Grover doesn't let on, and his evasiveness is really starting to creep Percy out.
It's only later on that Percy gets the full picture. One night, there's a knock at the door. It's Grover. Only it's Grover, but with furry legs and cloven feet. He appears scared out of his wits; apparently, "it" is following him. It turns out that the "it" in question is a Minotaur, a fearsome beast from Ancient Greek mythology: half-man, half-bull. Grover, Percy, and Percy's mom get into the car immediately and head off in the direction of Camp Half-Blood, with the Minotaur hot on their heels. In the ensuing struggle, Percy defeats the Minotaur, but not before his mom is turned into a flash of light that vanishes into thin air and his best friend Grover is seriously injured.