BoltBacker
Footballguy
Exactly.You may have heard the phrase regression (or progression) to the mean. Related to this is the concept that each individual player has their own mean that they regress or progress towards.
So the study was focused on that. Trying to find a players true mean in terms of yards per carry. That mean cannot be found until the player has enough volume which was about 2000 rushing attempts.
The point being that one season is not a large enough sample size to find the players average or mean yards per carry. Two seasons might be enough to be reasonably close to that, three years would be a sample I would have more confidence in. 3 years discarding the rookie season stats would be more reliable than that.
So Richardson's agent would argue that his mean could be 5y/c we just haven't had enough carries to see it yet. In fact he has ~600 carries so deserves six(?) more years of carries before we know what his mean would be.
Would you have more confidence in 4 years that 3?