Virginia Tech’s offensive struggles are well-documented. North Carolina’s defensive woes are readily apparent.One of these groups is bound to be feeling a bit better by the time the two sides wrap up their Atlantic Coast Conference game Saturday in Chapel Hill, N.C.Virginia Tech (2-2, 1-0 ACC) has averaged just 20.3 points per game compared to North Carolina’s 46.5. The top rusher for the Hokies is Keshawn King with 179 yards on 29 carries.But North Carolina (3-1, 0-0) has given up 39.5 points per game. Even in victories over Florida A&M (56-24), Appalachian State (63-61) and Georgia State (35-28), the Tar Heels have had to put up a lot of points to win.”Defensively, we’re very disappointed,” Tar Heels coach Mack Brown said. “We have very good players and coaches.”North Carolina was shredded by Notre Dame in Saturday’s 45-32 loss, adding to the list of defensive failures. Brown said he maintains confidence in defensive coordinator Gene Chizik, who returned to the Tar Heels this season five years after stepping away following two seasons on the staff of Brown’s predecessor, Larry Fedora.”It’s obvious we’re making mistakes,” Brown said. “We can’t do that.”The Hokies have had extra time to try to tweak their offense under first-year coach Brent Pry. They suffered a 33-10 home loss last Thursday to rival West Virginia.”This is kind of where we are as a team right now,” Pry said. “We can’t leave too much to overcome in any phase.”Virginia Tech’s 15 penalties in its latest game were among the snags.