Well there isn't any set rule, but the blindside flanker is generally put there for a reason. If he has the mobility, then why isn't he playing openside or 8-man? But being the larger player, he (or she) generally doesn't have the mobility. There are physical laws at work which -- all else being equal -- dictate that big players simply aren't as mobile as smaller ones. The odd player (Richie McCaw?) who has both size and the mobility to play openside is a nice problem for a coach to to have, but they are very much the exception rather than the rule.
it dosent really matter the size if u have the determination to play that position then play there. I am the smallest on my team I play on a high school sr girls team im 5'2 and only 115-120 pounds so not big at all im not able to play this season due to injury but fall season I was a starter openside flanker number 7 so size really dosent matter. most of the teams we played I was tackling people easily over twice my size so size is no factor in rugby
In these days of giant back rows there's often no difference between any of them. It just depends on who plays where.
