The Pts/60 measures are how that player did in that given year. So, from above, players in the top quartile average 2.4 pt/60 in their contract year and their contract year only, and those same players averaged 1.9 pts/60 the year before. These are not career averages - just averages across players for that year.

There is no survivorship bias, because it is the same players being examined in all the years. There is no any look-ahead bias, because players are aware of when their contract year is, and we're only looking at performance in a specific year and seeing how it changes. You are correct, however, that we could be capturing something like an age profile. This is discussed in the article above. I'm sure we're capturing the effect of an age profile for RFAs. However, UFAs are generally past their peak. There is no way to reconcile a flat trend before the contract year and the spike up in the contract year with an age profile.

Again, if I've misunderstood what you've said, let me know.

If you don't do this, you are merely looking at the YoY trend. Top quartile players may show an uptrend for reasons of age (entering their primes) and not related to CY effects at all. These other factors either need to be controlled for or performance should not be based on the entire sample.

Your concern, as I understand it, is that we might be observing survivorship bias because there are players dropping out of the dataset in their contract year and the year after, and these players are below average for their quartile, thereby bringing the average up after they drop out.

If I haven't got it right, let me know.

But, there are no players dropping out in these data. We are only looking at players who signed a contract, and then compare the performance of those players in their contract year (the last year of their old contract), to the years leading up to it, and the year after.

So, if there were 12 players who signed a contract in the data, we sorted them by how well they did in the last year of their old contract. The top 3 would then be in the top quartile. We then looked at how those 3 players did, on average, in the years leading up to the new contract, and in the first year of the new contract. So, there is no survivorship bias. Nobody drops out of the data - the quartiles contain the same players in the CY year as well as the CY+1, CY-1, etc years.

I hope this answers your question. As I said, if I've got your question wrong somehow, let me know.