rivalries that belong to the fans

we need the opportunity to create relationships between teams, including rivalries

every season, each fan* of each team should get a vote^ towards which other team is the most... hated is not the right word, more like which team the fans would most like their team to beat, which contest means the most to them. these reasons can be unspecified and speculated on and/or generated by the fans.

the team with the most votes will then be designated as that team's rival team. players get a boost when playing against their rival team.

*a fan of a team is someone who has selected that team as their favourite. rivalries are for the fans who love their team, not the owners who love money
^a single vote each season. no fan stands above another

some ideas for implementation (aware that it may not be able to be exactly like this):
1. asymmetry is ok (e.g. the Owls can designate the Howlers as their rival team, but that does not automatically mean the Howlers have the Owls as a rival team)
2. votes are cumulative (e.g. 10 votes for the Pyres after S3 still stand for S4, and will go into the rivalry mix with votes in S4). it might take many competitions to overcome an old rivalry. there is probably a maximalist version that has weighting that decreases the value of old seasons, or where you have fierce rivals and lesser rivals and etc. based on the ratio of votes, but maybe just a big old pool with one overall rival for now is good.
3. maybe only particular stats are boosted (like physicality? stats that reflect a greater intensity and clamouring fans)
4. this vote can be changed as many times as possible up until a deadline (end of the season perhaps or opening day of the next season?) at which point all votes are recorded and rivalries ratified or altered
5. rivalries are recorded on a team's page. it is one of the most identifying features of a team.
6. perhaps who each fan voted for is recorded as their personal rival team too? to reflect that maybe fanbases are not unilateral in their ire
7. one vote for each fan for only their favourite team
8. if a fan changes team, any old votes that have been registered (i.e. in a previous voting window) are continued. the passion was once real. but any pending votes are either only for their new team (there's another reason to switch!), or forfeit entirely (probably too harsh)
9. if a fan has no favourite team, they forfeit the right to contribute to a team's stat boosts in a rivalry, but they may still have a personal rival team by voting in the usual way