...
Select a file revision from the History menu and click the Contributors to open a drop-down list of all contributors who changed this file up to this revision.
In the list you can see contributor name, number of lines they changed in this file and number of their commits that modified the file. If a contributor is a Stash user, clicking their name will take you to contributor's Contributions graph where you can check contributor's overall performance and all their commits and pull-requests made in the last year.
...