It’s all about Purposeful Movement
“You must pin your free hand!” Not necessarily. In this picture below, a still from one of Adam Jeup’s (pronounced “jewp”) training videos, you can see that Adam has purposefully pinned his right arm while executing a rifle toss with his left. There is a reason he did this: “military flavor,” enhanced power to the toss, etc.
Adam could have chosen to place his right arm at any point on the clock (let’s say 9:00) and the move would have been a variation and still looked good if he could keep his right arm steady in that position. He also could have kept it moving from the 6 o’clock position pictured to 12 while executing this movement: another variation- layered body movement under the rifle work. This is difficult stuff to do, though, and is for advanced Drillers who can easily manipulate the rifle and then create variations/other movements.
The picture below, from army.com, shows the US Army Drill Team during their performance at the Joint Service Drill Competition probably in 2009. The point of the picture is to show you the free arms of three of the soloists. Do you see how they are in different places? They all should be pinned: it looks cleaner, keeps the “military flavor” theme that is the number one requirement for the service drill teams and also does not take energy away from the toss.