[Bill_B]

You won't have to go very far into Electrical Engineering before you find out that sparks at disconnection are largely due to inductive loads, viz. motors and transformers. Inductors try to maintain current in their circuits. To do that voltage will increase across a switch as it opens and increases resistance. Eventually the switch "wins" and makes a very high resistance in the air gap, but not before a large inductor load tried to jack the voltage very much higher than usual. Sometimes the voltage spike will actually get high enough to cause current to jump the minuscule air gap as a switch opens. Result? Sparks. Not usually a good thing, so quite a bit of E.E. talent has been devoted to this solving problem.

As it applies here, if motors weren't running when you pulled the battery plug, there is very little chance of noticeable sparking. Voltages in FRC robot-land are usually quite low, so bare-skin contact is not a great danger. However, if the hand in contact has metal jewelry or tools in it, the danger of high current short circuit should not be ignored. I sometimes think that a you tube video of egregious electrician's behavior should be made to convince "kids" how easy and calamitous such short circuit "welding" can be.