If someone working for a large corporation like Walmart or Target showed up for work dressed up to promote a political candidate or cause, that employee would be sent home or fired.  Businesses work to serve everyone and alienate no one.  After all, both Democrats and Republicans buy food and soap.

The NFL made a huge mistake by not taking action when the kneeling first occurred.  Now their brand and ability to make money are tarnished.  They are loosing fans and money because their inaction has alienated half of their fan base.

Football players have to the right to free speech on their own time.  Not on company time.  Save it for their twitter feeds.  

The court decision cited on the pledge was when a government institution (a school) coerced actions.  The NFL (not a government institution) can coerce participation by its employees.