It obviously depends how well managed the field is, but on a playing field that is professionally managed grass is typically safer. Obviously turf is easier to maintain so for facilities that don’t have the time, money, or expertise than an artificial field is safer. I don’t claim to be an expert but I took majored in Landscape management at BYU and took a handful of classes on this kind of stuff along with a sports turf class and a lot of studies show grass is actually safer.