Studies confirmed the existence of a social norm that one cannot simultaneously support two competing groups or teams

You Can’t Root for Both Teams!: Convergent Evidence for the Unidirectionality of Group Loyalty. Daniel J. Kruger et al. Evolutionary Psychological Science, https://link.springer.com/article/10.1007/s40806-018-0178-0

Abstract: Four studies tested the existence of a social norm that one cannot simultaneously support two competing groups or teams. Our evolved coalitional psychology should be sensitive to individuals expressing mixed loyalties between rivals, as they represent substantial threats for defection. Study 1 manipulated confederate attire and demonstrated that public displays of mixed loyalty provoked more attention and reactions than displays of consistent loyalty (n = 1327). Informants (n = 31) in the same population interviewed for study 2 agreed with the norm and cited the norm violation as the cause of reactions. Study 3 provided a more systematic and comprehensive assessment of affective and cognitive reactions to mixed and matching loyalty displays with an on-line survey of participants (n = 325) in the respective states of the rival universities. Study 4 examined naturalistic reactions (n = 318) to social media advertisements suggesting mixed loyalty to the two rival teams featured in the first three studies. These diverse methodologies provided convergent confirmatory evidence for the proposed social norm.

Keywords: Teams Intergroup perception Evolutionary psychology Loyalty Observational methods