After playing outside he vomited wild grass, then undigested kibble, then loud diarrhea, now watery stool, no eating, no fever, no blood

Vomiting and diarrhea after eating grass may be acute gastroenteritis; grass fiber irritates the stomach wall and triggers vomiting.

Frequent vomiting can lead to gastroenteritis; try pet-specific anti-inflammatory and anti-diarrhea medicine such as amoxicillin-clavulanate, neomycin, smectite or bismuth subcarbonate. If it eases, offer a little warm-water-softened kibble.

If not, take the cat to a vet for examination and fluids to avoid long-term electrolyte imbalance from vomiting and diarrhea.