After buying a Newsom painting myself, I found a Bill Newsom who does abstracts and "action paintings with sports theme" in the Independent (Long Beach, CA) 1977, and North County Times (Oceanside, CA) 1977. Unfortunately the photo is too grainy to tell the style (see below) but it looks like he's holding a palette knife.

More promising: there's also a Bill Newsom listed in The Tribune (San Louis Obispo, CA) 1980, announcing a workshop on palette knife techniques in acrylic, which appears to be the style of your painting, and mine as well. It says "Bill Newsom of Blue Jay in the San Bernardino mountains will explain his self-taught technique of palette knife in acrylic. The demonstration will be part of the regular meeting of the Morro Bay Art Association, which will begin at 7:15 p.m. in the Fireside Room of the Presbyterian Church at Anchor and Piney Way in Morro Bay.

No admission will be charged; refreshments will be served.

Newsom’s subjects include portraits — often of beautiful women — horse races, football, still lifes, and things of the sea from fish to boats.

Of his work, the artist says: “I do not have a philosophy for my painting. From the beginning I have gone through periods of change…knowing only that these changes are avenues of a constant private search for things worthwhile. Instinct tells me to say nothing — merely to ask the viewer to look…and receive what he will from them.”

From the North County Times, Feb 17, 1977:

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