The head and arm control is an outstanding control position we use frequently in FSD. One arm is positioned against the opponent's neck, and the other under-hooks or under-wraps his arm. The under-hook is typically done in FSD at the opponent's elbow, but it can also be done at the shoulder as is normally done in wrestling. The head is kept low, protecting it against strikes coming from the opponent's free side. However, with pressure on the neck, continuous movement, and offensive techniques, it's unlikely the opponent will be able to strike at all.
There are numerous ways to get the head and arm control. One of the most effective from outside of the clinch is the smack and hack, a technique that immediately results in the control. Using a crash against some punching attacks will also put you inside the opponent's arms, where you can quickly transition to the head and arm control.