How many players from each team are on the field during a rugby union match?

How to get close to this number

This is one of the few field sports that breaks the eleven convention, and it breaks it upward. A game built around contested possession in physical contact needs more bodies than one built around space, so the count runs above the football standard rather than below it.

The split in the explanation is the structural detail: eight forwards and seven backs, two groups with almost entirely different jobs and body types. Few sports divide a team into two such distinct sub-teams, and it is why positions in this sport are not interchangeable in the way a football team's outfield players broadly are.

The comparison with the other code is where confusion lives. A closely related sport plays with thirteen on the same size pitch, which speeds the game up by reducing defensive coverage. Two sports sharing a name, a ball and most of their history differ by two players, and that difference produces genuinely different games.