Use case

Return the number of times that the resolution of an issue was changed to "Rejected".

Expression

Create and configure a Smart field using this expression in Jira expression  mode:

 issue.changelogs.filter(changelog => changelog.items.some(item => item.fieldId == 'resolution' && item.toString == 'Rejected')).length

In case you have other statuses and resolutions, feel free to change these arguments: " item.fieldId == 'resolution' && item.toString == 'Rejected'"