Without more details that aren't in the article, it's impossible to know what caused this rollover, but the story as written is a very common roll over. The way it inevitably happens is that the tractor is hitched to the load with the hitching point above the level of the rear axle. Typically someone either hitches to the top hook on a quickhitch or hitches to something fastened into the 3PH but has the 3PH raised so the attachment point above the axle. 3PH are only designed to be safe for pulling when the resisting force is applied at ground level (rake, etc) or below ground (plow). When you loop a chain to the 3PH, the point of application of force is as high as that hitching point is, NOT the tree/stump/rock/post stuck in the ground. Always hitch a load at or below the height of the axle. Almost all tractors provide an attachment point to facilitate this.What exactly caused it to roll? Also, no ROPS on this tractor?