USSSA Tag Out Scenario

[OKExplorist]

In the last game of a seven game day, I found myself smack-dab in the middle of controversy. Here's the info:

R1 on first. Me in B. Pitch is released. R1 stealing second. Catcher rockets ball to F6 as she comes in to cover second. R1 jumps up a bit to slide into second. As she does, F6 makes the catch at knee height on the first base side of second and applies the tag to the back (underside) of R1's left leg as R1 is going to the ground to enter her slide. As a result of the tag being under the leg both R1 and F6 end up going to the ground. I hesitate, see the play twice and call the out. The crowd and coaches erupt in disgust. I stay on the play as F6 stands up with the ball in glove.

First base coach calls time and comes to me and calmly asks me to explain the call. I do. He's not satisfied and said the ball was on the ground. I told him a didn't have that. He requested I ask for help. I did. My partner said he did see the ball on the ground as F6 was getting up but was blocked on the tag by the catcher. We concluded he didn't have enough information to give me to change the call. I step aside and confirm the out. Two outs.

We resume play while a bunch of belly-aching comes from the fan. After third out, the third base coach has to walk by me to get to his dugout. He asks me to explain my call. I get about three words into it and he erupts about how the ball was on the ground the whole time. I stop my explaination to tell him he can either listen politely to my explanation or watch from the parking lot. I then turned away to take my position. Halfway through the next half-inning he was still complaining loudly (not directly at me but about me) to a fellow coach in the dugout.

You make the call......
1) What would you have called on the pick-off attempt?
2) Would you have changed your call based upon your partner's observation?
3) Should the coach have been ejected and why?