And when he says live, he means it.
None of this stop at the whistle, helmets and shoulder pads only stuff. That's for teams who can tackle.
"We actually tackled live to the ground," Jancek said, "which you normally don't do on a bye week."
Missed tackling is still a glaring issue with the end of the season fast approaching. At 4-6, Tennessee must win out to reach a bowl game.
If the Vols' defense can patch up, they just might have a shot with games against Vanderbilt (5-4) and Kentucky (2-7) left.
"It's just been such a big issue for us," Jancek said. "That's something that has to be addressed now."
As many encouraging signs as there have been in Butch Jones and staff's first season, Tennessee shows week after week that it still has significant strides to make on defense.
Jancek inherited a defense that ranked 107th in the nation in points allowed per game last season under the direction of Sal Sunseri's 3-4 scheme.
In others, it hasn't.
Jancek shored up a pass defense that gifted Troy 496 yards through the air last season.
But quarterbacks have gobbled up 657 rushing yards against the Vols. They ran for 225 a year ago.
"We need to improve," Jancek said. "If we don't, we're going to suffer."
The Vols have suffered plenty already.
Tennessee has coughed up 987 rushing yards in its last three games.
Luckily for the Vols, the roughest waters are behind them. All three hair-pulling defensive performances came against top-10 opponents.
Still, that shouldn't be an excuse for missed tackles.
"Regardless of who we play, that doesn't change the fact that I'm accountable to do my job," Tennessee defensive line coach Steve Stripling said. "This is the league we play in."
Stripling and defensive coaches' job this week is to find consistency.
While live-padded practices are an attempt to revamp energy, the Vols are also getting back to basics during the bye.
Jancek is pleased with the progress so far.
"From yesterday to today, I thought our guys came a long way," he said. "They did a much better job and were much better with their fundamentals."
Tennessee entered the bye week fresh off a 55-23 loss to No. 7 Auburn. A game where the Tigers ran over, around and through the Vols' flimsy defense.
Auburn piled up 444 rushing yards. Quarterback Nick Marshall led the way with 214 and running back Tre Mason chipped in a modest 117.
Auburn runners bolted through arm tackles. There were countless whiffs in open field. The mistakes were glaring.
But tackling issues have been there even when it's not as obvious.
"It's been inconsistent all year," Jancek said. "Even in games where we have statistically performed well. We need to fix the issue."
Identifying the issue and fixing it are two very different things.
Though no coach will say it, Tennessee's defensive struggles could be a simple personnel issue.
Potential NFL linebacker Curt Maggitt opted for a medical redshirt after tearing his ACL last season. Defensive tackle Maurice Couch was banned from playing again by the NCAA for accepting cash benefits. Defensive tackle Trevarris Saulsberry is struggling to stay healthy.
The mishaps keep piling up. And it's forcing more and more youth onto the field.
Coaches will say, though, that it's not an excuse.
"We have great kids and we're not going to ever give up," Jancek said. "We're going to keep pushing them and working them hard. We expect them to get better. We owe that to the seniors and the guys who have chosen to play at the University of Tennessee."
John Jancek, per university