Don't ever have someone hold the mast base. If the base comes off the ball, the person is sure to lose teeth. If the mast needs a "safety", use a piece of line.
One other note, never have anyone "Catch" your mast as you are lowering it. Have your helper stand to the side until you can hand the lowered mast to them. Tell the helper directly, "stand to the side until I can hand the lowered mast to you. If I lose control, let the mast drop. It will not hurt the mast, but it will hurt you if you are under it." I can not tell you how many people I have seen hit over the years trying to help a friend.
Stepping or lowering a mast is best done with help. The 20 mast is heavy and as stated needs to be rotated to lower correctly. If your mast rotation bar is at the tramp level, remember to disconnect this line first as this alone can pull the mast off the ball.
I use a winch hooked to my forestay to assist raising and lowering the mast. Either way, it is important for the assistant to realize that they are helping to keep the mast on the ball. That said, if you raise the mast quicker than they can crank, the forward pressure is lost and the possibility of lifting the mast off the ball increases. Using the pin may help to limit lifting the mast, but as stated, the pin is not failsafe.
Take your time, use help, and don't ever become the human mast crutch.