Passer rating is an imperfect measurement of a quarterback, but to the extent that it shows how well a passer is playing, it points to something puzzling with the Colts this season.

The Colts’ starter, Anthony Richardson, has the lowest passer rating in the NFL among the 32 quarterbacks with enough pass attempts to qualify. The Colts’ backup, Joe Flacco, ranks first.

Richardson started the first four games of the season for the Colts and completed 39 of 77 passes for 654 yards, with three touchdowns and six interceptions, for a league-low 60.2 passer rating.

Flacco replaced Richardson in Week Four and started Week Five and has completed 49 of 70 passes for 527 yards, with five touchdowns and no interceptions, for a league-high 115.6 passer rating.

The Colts see Richardson as their franchise quarterback and see developing him as their top priority, and so there’s no real competition in Indianapolis. Flacco is there to support Richardson and to play well when Richardson can’t go, and Flacco has done that very well.

It’s the second straight year that Flacco has done very well as the backup to a highly touted starter; last year he became the Browns’ starting quarterback after Deshaun Watson got hurt and played much better than Watson, leading the Browns to the playoffs in the process. He was rewarded for that by the Browns not even offering him a chance to return as Watson’s backup, because the Browns know Flacco is better than Watson and the Browns know their fans know Flacco is better than Watson, and they don’t want the fans chanting Flacco’s name while the team continues to cling to the sunk cost of Watson.

But Flacco’s strong play for a second consecutive season on a second team raises the question of why the best free agent offer he got was a one-year, $5 million deal to be a backup in Indianapolis. Perhaps some team should have made Flacco a better offer, with at least a chance to compete for a starting job. For two years in a row, Flacco has balled out when given the opportunity.