15 rinks the puck detector has never seen. Your clicks train the next detector; nothing here is scored. Click the middle of the puck. One click saves it and moves on. If you can see no puck in this frame, press N. If something might be the puck but you cannot be sure, press C.
Click = puck centre (next frame). N = no puck visible. C = can't tell. Left arrow = back (then click again to redo).