The back foot defence answers the ball that's too short to drive but too straight to leave: the back foot goes back and across toward off stump, you stand tall, and the ball is met with a straight bat and soft hands directly under your eyes, dead-batted into the pitch. It's the shot that buys survival on quick pitches — and it's built almost entirely on the first foot movement.
Short of a length, on the stumps or threatening them, doing enough off the pitch that pushing at it is a slip catch. If it's wider, leave it or cut it; if it's fuller, defend forward. The back foot defence exists for the ball that would hit the top of off if you missed it.
Length decides. Full enough to meet at a comfortable stride forward → front foot defence. Short enough that it arrives above knee height off the pitch → back and across. If you're unsure, the ball hitting your glove or splice usually means you went forward to one you should have played back.
Straight down into the pitch, within a metre or two of your feet. If it's carrying to fielders, your hands are too hard or you're pushing at it.
Sticks works anywhere you can swing a bat — at the nets, or at home with nobody bowling. It watches through your phone and speaks this kind of coaching out loud, one focus per shot — in English or Hindi. Video never leaves your phone, and it's free while Sticks is in beta.