I don't recall anyone complaining when Phil Jackson was handing out books on Bhuddism.
If Pete Carroll took all his players to do yoga or something and someone was like "Heck no." people would say the guy wasn't a team player.
My understanding is that the team that crams religion down your throat is probably BYU.
Does anyone know if Arian Foster does Christmas? If he does he's sorta a fair weather atheist, right? Does he celebrate St Valentines Day? Does he honor Irish Catholics by getting really drunk on St Patrick's Day? Does he celebrate MLK Day?
BYU has a lot of Mormons, so they don't really have to cram anything.
Lots of people do secular Yoga. Lot of people practice mediation that has no religious content. These are practices that have empirically been shown to have benefit. The also do not challenge anyone's already held worldviews, unless you choose to do those practices with people who like to inject religion. In fact, quite few Atheists also consider themselves a form of Buddhist with no real contradiction due to the nature of Buddhist philosophy (or Zen Buddhism, which I assume is Jackson's thing).
Holidays are irrelevant. Why would being an atheist stop someone from celebrating holidays with other people? I could ask why Christians celebrate a holiday on Dec 25, a day chosen due to being during Saturnalia. They can celebrate whenever they want if that is what they enjoy. The fact that Dec 25 isn't very compatible with the stories in the Bible doesn't really matter. People are free to enjoy the traditions they want. Why should Foster be anti-Christmas just because he doesn't believe in any gods? Christmas has become part of secular culture, even in some Muslim countries.
If we are talking football though, religion is a regular problem and players not in the establishment religion are put in a lot of awkward situations in HS and even in some colleges. Not really an issue in basketball.