Issues that could cause the Vikings to red-flag a player as a character risk, and how the team would screen for them:

Arrests/school discipline: In addition to the background checks the NFL does on every player who attends the February scouting combine, the Vikings paid for their own security checks.

Team disciplinary action: The Vikings conducted face-to-face interviews with every player who attended the Senior Bowl and scouting combine, and they routinely interview those players' college coaches.

Psychological issues: The Vikings paid an outside agency to conduct psychological testing of players and develop personality profiles.

Positive drug tests: Even if a player didn't attend the scouting combine, these would turn up in any team security check.