We get 6 months weekly average pull request throughput of each team. We call this the "Baseline Throghput". If a team has more (or less in some cases) pull requests open than the baseline, we consider that a "too many".

Too many Open Pull Requests can signal taking on too much work, scope creep, change in priorities and unexpected issues/bugs coming into the sprint. It’s good to keep an eye out of the number of Open Pull Requests since it’s a great indicator of the team’s current workload.