That appears to be a direct tie-in to some of his past health questions (knee, back).
We'll wait to see the fine print of the contract, but it would make sense to think that the playing time stats are in the 80 to 90 percent range (if Vollmer hits those numbers, he'd cash in). With this in mind, ESPN Stats & Information passed along Vollmer's offensive playing time statistics from the first four years of his career:
Based on Vollmer's first four seasons, he would project to collect about half of his roster bonus money in the new four-year contract. Naturally, it would be a win-win for Vollmer and the Patriots if he collects it all.