... Apparently I should press to lock focus on the subject and release - the camera will keep the focus locked until I press the button again?
Well, it depends... Think of BBF as, AF-C "on demand": as long as you keep pressing the button, you're in AF-C. Release the button and everything stops. You can press-and-release if your subject is stationary but you would probably want to press and hold, for continuous focusing, if the subject is in motion.
So when shooting an active subject (sports), I should lock on the player, let go (using continuous focus) and shoot. Is this correct?
It depends on how you want to frame the shot and whether the player is in motion or not...
If the subject is in constant motion, but I can keep one or more focus-points on the subject, I would keep the button pressed and fire the shot (
a la AF-C).
If the subject is stationary and I wanted focus and recompose I would press the button to focus on the player, release the button, recompose and press the shutter button (
a la AF-S).
The only thing I
don't like about BBF is that it over-rides the
Focus Lock Priority - Focus setting in the menus. Meaning the camera will take a shot even without having achieved focus-lock. That being the case I have to pay close attention to the focus-lock indicator-light in the viewfinder; or I guess I can ignore it and take my chances with out of focus shots. This is the primary reason I switch back and forth so frequently between BBF and Shutter-Button Focus. Sometimes I can deal with how BBF works, sometimes I can't. Fortunately, for me, I don't have any issue switching between the two.