Answer: rivalry

AnswerCrossword Clue
RIVALRYIt's not unusual among siblings
RIVALRYArmy versus Navy, e.g.
RIVALRYIt's common among siblings
RIVALRYCompetition.
RIVALRYCompetition
RIVALRYYankees vs. Red Sox, e.g.
RIVALRYSiblings may engage in it
RIVALRYKeen competition between teams
rivalrythe action, position, or relation of a rival or rivals; competition
rivalryinstance of this
rivalrycompetition, also RIVALITY