We'll have to agree to disagree on that. I ran track in college and have a minor degree in athletic coaching, including studies in anatomy and kinesiology. If you "pinged" your hamstrings simply running, you either weren't stretched/warmed up properly or had an abiding anatomical imbalance working against you, perhaps training related. Everyone has weak spots, though, and it takes a good trainer with scientific knowledge to identify them and prescribe a corrective regimen aimed at mitigating injury risk. The rest is on the athlete's shoulders to manage his body effectively. Developing flexibility, stretching and warming up properly are part of that -- especially important toward avoiding soft-tissue pulls and strains.
My point is these guys are professionals, with professional conditioning coaches and trainers. I will assume that with all the millions the Pats have invested in him, whatever inherent risk Gronk might have for hamstring pulls has been addressed by his conditioning coaches and trainers. How well he has managed HIS end of the responsibility I think might be open to question.