Looks like an engine failure - a very rare occurrence nowadays. Considering the pilot was climbing through 100 feet, a low inertia rotor system and in the middle of the Height - Velocity diagram (Deadman's Curve) - a superb job by the pilot for everyone to make it out ok.
http://wjhl.com/2016/06/03/wellmont-helicopter-crashes-in-mountain-city/
http://wjhl.com/2016/06/03/wellmont-helicopter-crashes-in-mountain-city/