Williams played in 56 matches in 2015, losing only three. Sports Illustrated editors noted that Williams was being honored not just for her performance on the court, but also her tenacity, maturity and sportsmanship.
In forums such as Horse Racing Nation, fans argued that American Pharoah was more deserving because the thoroughbred had won the first Triple Crown in 37 years.
SI says the award recognizes "the athlete or team whose performance that year embodies the spirit of sportsmanship and achievement." But, of course, a racehorse isn't a person. Should American Pharoah have even been considered?
The debate led The Times' sports editors to wonder whom its readers would have chosen.
A tweet from the @latimes account asking readers to vote in an online poll was quickly met with a backlash. Readers took issue with the headline -- "Serena Williams or American Pharoah: Who is the real sportsperson of the year?" -- and the pairing of SI's cover photo of Williams with an action shot of American Pharoah.
The headline and tweet didn't make clear that the poll was prompted by SI's selection of Williams versus its readers' support for American Pharoah.
American Pharoah was one of the magazine's 12 candidates for Sportsperson of the Year. The horse finished first in the SI reader poll, with 278,824 votes. Williams came in 11th in the reader survey, with 5,520 votes.
Readers believed The Times itself was comparing Williams and the thoroughbred and found that offensive.
In response, Times editors changed the headline to read: "Are fans right to be upset that Serena Williams beat American Pharoah for SI Sportsperson of the Year?"
And the article now features only the photo of Williams.
The @latimes account tweeted the update.
Sports Editor Angel Rodriguez said the poll was intended to add to an ongoing discussion over the Sports Illustrated selection.
"We are comparing Williams' accomplishments over the last year to American Pharoah's in the context of the SI award," Rodriguez said. "It's about who actually deserves the award and who should be eligible for the award."
The Associated Press Sports Editors group is weighing the same question. On Monday, the group began the voting for its sports story and athletes of the year. An email asked members: "What event should be named the AP's sports story of the year, and who should win male and female athlete of the year? And, can a (male) horse be athlete of the year?
"It's up to the sports editors of AP members to decide."