Hermione had just come in, wearing her dressing gown and carrying Crookshanks, who was looking very grumpy, with a string of tinsel tied around his neck.
“Don’t bring him in here!” said Ron, hurriedly snatching Scabbers from the depths of his bed and stowing him in his pajama pocket.
But Hermione wasn’t listening. She dropped Crookshanks onto Seamus’s empty bed and stared, open-mouthed, at the Firebolt. Rowling, J.K. Harry Potter and the Prisoner of Azkaban (pp. 90-91). Pottermore Publishing. Kindle Edition.

But before Hermione could answer, Crookshanks sprang from Seamus’s bed, right at Ron’s chest.
“GET — HIM — OUT — OF — HERE!” Ron bellowed as Crookshanks’s claws ripped his pajamas and Scabbers attempted a wild escape over his shoulder.
Ron seized Scabbers by the tail. Rowling, J.K. Harry Potter and the Prisoner of Azkaban (p. 91). Pottermore Publishing. Kindle Edition.

Harry let go of the broom, which just floated there, and pulled out his wand and did an area wide stun to all participants. Then called an emergency elf to get both their head of house and the Mediwitch stat as he did every emergency care charm he had studied on his friend’s chest to stem the blood flow coming out of the tears from Hermione’s bloody cat.

Crookshanks was put down as a danger to all around him.
His mistress was fined two-hundred galleons to be paid to the Weasleys for her uncaring nature where her own pet was concerned. And was given a month’s detention scrubbing backsplash tiles in every girl’s lavatory without magic. And being watched by a guardian elf with silencing charms and earmuffs making constant statements about the rules where doing harm to other students was concerned.

Ron spent the rest of the holiday in the infirmary getting treatment for the cat tears in his chest.
Scabbers spent that month getting nerve treatment under the care of Hagrid, before running off to get away from the Grim on the grounds. A Grim, who later lost interest and left for a tropical island and fairer sexes.