I was just thinking about this rule we changed a couple of years ago...
13.4 - Any veteran player whose contract has not expired must be protected or cut with a salary cap penalty unless they have a DUR rating (durability) is no more than 3 (i.e. is 3 or less) as noted in Rule 14.14b.
Originally, this rule was changed from 3 games to a durability of 3. I think we changed it because some players played very few snaps but played 4 or more games and we weren't allowed to cut them without a penalty. I think it was a good decision.
However, this rule does not work for backup QBs. For instance, I was just looking at Jarrett Stidham. He played in only 3 games but has a durability of 10. I would be able to cut him under the old rules, but not the new rules. I think this needs to be fixed. Perhaps the rule should read no more than 3 games OR a durability of 3 or less. Just FYI - this does not apply to anyone on my team this year - not trying to pull a fast one. But it may hurt others in our league this year or eventually.
Before it was changed, the rule was four games. Four games on the active roster is 25% of the season. It gets rounded up to 30% in the game, or a Durability rating of 3.
The Durability rating is based on games on a NFL team's game day active (46 player) roster. While Stidham only appeared in three games, he was on the active roster all 16 games. Hence he gets a Durability rating of 10.