The assault happened at Ralston Park, near Third Street and Grove Avenue, around 2 p.m. Sunday.
Officers say Damien Galaviz, 29, was there for his young niece's birthday party. He approached Robert Carranza, 43, and asked him not to cause any problems.
That's when investigators say Carranza stabbed Galaviz several times in his arm.
The victim was flown to a Modesto hospital for treatment.
The suspect was seen leaving the area in a white Kia with the California license plate number DP195AZ.
Police believe Carranza is still armed with the knife used in the attack.
