http://profootballtalk.nbcsports.com/2015/09/07/report-grigson-makes-decisions-against-paganos-wishes/
But the Indianapolis Star reports that Grigson's tendency to make decisions that run counter to Pagano's wishes has become a real issue with the Colts. According to the report, Grigson inserts himself in lineup decisions, which are usually made by the coaching staff without interference from the front office. That included Grigson getting involved in the changes the Colts made at center last season, changes that not everyone on the team was on board with.
Usually when there's a rift between a coach and G.M., it's because the team is flailing and each man blames the other. But the Colts have made the playoffs in each of Grigson and Pagano's three seasons together. If the team continues to play well, Grigson and Pagano can probably push any differences they have aside. If the Colts take a step backward this season, however, it seems unlikely that Pagano will be getting a new contract. Instead, the Colts will be getting a new coach.