As our predominate grass species, annual bluegrass produces a relatively moderate amount of thatch.

From URI website - Thatch is a tightly intermingled layer of living and dead stems, leaves and roots which accumulates between the layer of actively-growing grass and the soil underneath.

Between most of our courts is bentgrass and this species produces lots of thatch. 

Courts 13-15 were just dethatched.  The top picture shows them yellowing where the thatch in the bentgrass has been agressively removed.  The bottom picture is courts 15-18, one week after thatch removal.  It was just as yellow as courts 13-15 - but within a week it looks almost fully recovered from the aggressive treatment.