Oscar Matthew "Battling" Nelson (June 5, 1882 – February 7, 1954), was a Danish-born American professional boxer who held the World Lightweight championship.

In 1913, he married Fay King, a cartoonist who did his portrait for Nelson's 1911 guide The Wonders of the Yellowstone National Park.

He fought for the vacant lightweight title against Jimmy Britt on December 20, 1904, but lost a twenty-round decision.

Finally, in the forty-second round, Nelson hit Gans below the belt causing him to lose the fight by disqualification.

Eventually unable to see due to the accumulation of punches, Nelson lost the title when the referee stopped the fight in either the fortieth or the forty-second round.

The second Gans-Nelson battle in Colma was the subject of a four-reel motion picture that played in major cities around the country.