That’s not booing for voting, that’s about making a divisive political statement on a freaking kid soccer game. When you bring your activism into non-political contexts, don’t get surprised when people don’t like it.
In some contexts, yes. A kid's soccer game is a place to hang out together and have fun, not to relitigate the major point of social disagreement of the day. If some kids from some other school behaved in an improper manner, deal with this problem directly, instead of taking your grievance out on unrelated community whose only crime is also being rural, so surely must be bunch of evil racists.
They kneeled before every game. They weren’t singling out any specific community.
And the school pushed as hard as it could to have the original incidents addressed (the same school has been reported for other similar incidents previously) and the league did not impose any consequences.