A potentially fatal slam. High risk of severe head injury.
A skilled grappler may employ this position effectively depending on the situation. However, standing headlocks are commonly used by those who lack grappling skills. This is often not only ineffective, but dangerous as this video demonstrates.
Another demonstration of the danger posed by hard surfaces. Slamming the head this way can easily prive fatal or life changing.
MMA fighter attempts triangle choke from bottom ground position. His opponent raises and slams him into the floor, resulting in a knockout. This is exceptionally dangerous and would most likely result in death on a hard surface.
This can be avoided by using techniques which break the posture of the person attempting the slam and bring them back to the ground, or by abandoning the technique as below. The slam is attempted by the same MMA fighter as the above video: