I am building a robotic hand, and I programmed the finger to close when the touch sensor is pressed, and release when the touch sensor is released. It did that with a loop block - 
but when I ran this the finger kept holding down. I could tell because when I tried to gently tug on the motor, it wouldn't budge.
Can anybody tell me what's going on?
Your code instructs the motor to continuously turn in one direction, and because you chose a motor block in the “on” mode, it will continue to turn even during the loop condition check. The loop condition says the loop will continue as long as the button is released (AFAIK, I don’t have an EV3 close by currently to validate this), which means that it does exactly the opposite of what you intended. Change the loop condition to loop as long as the touch sensor is pressed and you will fix this issue. Plus, once the loop finishes, the motor will still continue to turn; you would need to put a Motor block in the “off” mode directly after the loop.
What your current code does is to keep closing the finger until you press the sensor. This code may help.
You might need to change the 180 degrees boxes according to how many degrees the motor has to turn to close the finger.
You need to stop the motor after the loop
