NEW YORK (CBSNewYork)Giants co-owner John Mara says his team would have faced a boycott from fans last season if its players had joined Colin Kaepernick’s protest of kneeling during the national anthem.

“All my years being in the league, I never received more emotional mail from people than I did about that issue,” Mara told “If any of your players ever do that, we are never coming to another Giants game.’ It wasn’t one or two letters. It was a lot. It’s an emotional, emotional issue for a lot of people, moreso than any other issue I’ve run into.”

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Mara’s comments could shed some light on why Kaepernick, who led the 49ers to the Super Bowl four years ago, is still a free agent. While some have argued the reason is purely performance related, others have suggested the quarterback is being blackballed by the NFL for his controversial stand on social injustice.

Mara said the Giants never discussed signing Kaepernick, 29, because they were more focused on finding a potential long-term successor to Eli Manning. While they drafted California’s Davis Webb in the third round in April, they also signed ex-Jet Geno Smith, another former starter looking for a second chance.

Colin Kaepernick protest

Eli Harold, left, Colin Kaepernick, center, and Eric Reid of the San Francisco 49ers kneel on the sideline during the anthem prior to the game against the Dallas Cowboys at Levi’s Stadium on Oct. 2, 2016, in Santa Clara, California. (Photo by Thearon W. Henderson/Getty Images)

Kaepernick began kneeling for “The Star Spangled Banner” to protest racial oppression and police brutality in the United States. Players from several other teams later joined him, either by kneeling or holding up clenched fists during the anthem.

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Several Giants players admitted in September they were considering following Kaepernick’s lead, but ultimately they never staged any on-field protest. It’s not clear if they faced any pressure from within the organization. Coach Ben McAdoo initially said he would be “disappointed” in players who protested during the national anthem, but later changed his tune, saying he encouraged players to use the platform given to them.

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The 49ers selected Kaepernick in the second round of the 2011 draft. A year later, he led San Francisco to Super Bowl XLVII, where they fell just short to the Baltimore Ravens, 34-31. But the once-promising star has struggled mightily over the last two seasons, being yanked in and out of the lineup and going just 3-16 as a starter.

Kaepernick, who in March opted out of a contract that would have guaranteed him $14.5 million this season, has said through his representatives this offseason that he doesn’t plan to continue kneeling during the anthem.

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There have been reports that there is mutual interest between the Seattle Seahawks and Kaepernick, who would serve as Russell Wilson’s backup if signed.