Going by the images shown by user, it’s clear that the device is absolutely shattered in the front. But the user reportedly had music playing all the way through and the device didn’t stop even for a second. Even more surprisingly, the smartphone is still fully functional despite the nasty damage the front portion received.
Regardless of the outcome, we would strongly suggest against having your Galaxy S4 Active while using the lawnmower. We’re not sure if the more recently announced Galaxy S5 Active will live up to the incredibly high standards set by its predecessor, but it’s probably not a good idea to try.