The suspect is described as African American man about 5'9 to 6' tall, in his early to mid-20s, slender, with short brown hair. He was wearing a white t-shirt and blue jeans and a white baseball cap.
The woman was hit with a closed fist Monday afternoon at a strip mall on Blossom Hill Road.
In the "knockout game," people try to knock out unsuspecting victims with a single sucker punch.
Anyone with information is urged to contact the police at 408-354-8600.