To my understanding, rules to 7 ball have changed over time.
The original rules were like this: You call a side of the table prior to the break. Then, after the break, you may sink the balls (in rotation of course, 1 thru 6) in any pocket you choose. However, the 7 ball must be pocket in one of the three pockets on the side of the table you selected as "yours" prior to the break. Your opponent must sink the seven in one of the three pockets on his/her side. Safety shots were legal. There was no "ball-in-hand" awarded for a missed shot.
Rules have changed over time for television purposes, speeding up the game and showing run outs more frequently. Then, to reel in the frequency of run-outs, changed further. Now, one no longer needs to choose a side of the table. You simply play the game in rotation and need only to call one shot: the 7 ball. You are allowed to play safe once in a rack. All other shots must result in pocketing a ball. If a ball is not pocketed and safety is no called, the incoming shooter is awarded ball in hand.
Its all very easy now. One miss and the game is over.