As noted, settling into your root won't be enough, because the attacker is actively looking for leverage as well. Simple uprooting won't work either. You have to drop and interpose pun, then work the attacker's upper body. The results are much like sprawling and getting an under/over hold if you use hold golden ball, and look pretty similar. The difference is that you'll typically keep one leg a little farther forward. This makes you vulnerable to a single-leg, which is why it's so important to adhere and control the shoulders.
Taiji tactics should actually be fairly agressive. While you do tend to move after the opponent *starts*, you should be moving to intercept and adhere as soon as he commits. Too many folks simply wait around. What you want to use in combat is "throwing stones down the well," the principle that, once an opening occurs, you're absolutelu decisive about attacking through it and continuing until the opponent's reaction forces you to change.
You should learn to grapple to deal with the ground as well, but your TJQ work should never have a passive, overly soft character.
