The main goal of Zung Jung is to provide a game that is based on Chinese Classical, with a more modern scoring system, that has a balance between offense and defense. The name literally means The Middle Way, meaning not too defensive nor offensive; not too difficult for beginners nor too simple to master. There are rules that encourage offense, and some that encourage defense too. Zung Jung is not perfect, and I don't agree with every rule, but I think it's the best rule set available today.
For offense, there is the notion of what I'll call a par score, currently at 25 points. If the winner scores this par score or less, everyone else pays the winner that number of points. Since there is no extra penalty if you throw the winner's tile in this range, there is no large price to pay. This encourages you to go for a winning hand as long as you think your opponents are going for hands of that score or less.
Also, while you may be tempted to go out quickly, a win with no points is rewarded meagerly. You can't hope to win a whole game this way, as someone will almost certainly go out with a nice score pretty quickly once in a while, leaving your tiny score in the dust. (One 30-point win will overtake 29 of your 1-point wins, and even if you play a full game, that's only 16 hands.)
The points on scoring elements also encourage offense: By not having a large score for a concealed hand, you are encouraged to claim tiles to complete your scoring patterns. While you may lose points by claiming tiles for triplets (versus waiting to see if the tiles you need come from the wall), the potentially larger penalty you incur is the risk of your opponents deducing what you want from the completed sets in front of you.
Now for defense. The first rule that helps in this regard is not having a minimum score. If you think someone is going for something big or huge, you can try to go out quickly with any regular hand. This tactic can also be used when you are in the lead and want to stay there. Offense by way of defense.
The second rule that helps a little is the rule of same turn immunity. This says that if you throw a tile called for mahjong, but that same tile was thrown before the winner's previous turn, the person who threw it first is penalized as the discarder. This makes it safe to throw the same tile as someone else, but only if you do it right away.
Some other things that help with defense are also used in other modern styles. Orderly rows of discards show you the tiles that your opponents are unlikely to want, as does turning the claimed tiles.
If you are familiar with Riichi, Zung Jung is definitely balanced more for offense; but if you are familiar with Mahjong Competition Rules with its high minimum score, Zung Jung should seem balanced a little more toward defense.