Four days into training camp, quarterback Josh McCown and the Cleveland Browns offense have been performing at a higher level than anticipated by some outside of the organization – given that this is Year 1 in a new system and the Browns have three Pro Bowlers and one of the deepest defensive back units in the NFL.

It's given secondary coach Jeff Hafley some mixed emotions.

"I thought McCown had an unbelievable day," Hafley said after Sunday's practice. "He was dropping some balls in, making some throws. That excites us. We want to see that.

"But at the same time, we weren't happy. Because balls were caught on us."

While Joe Haden, Donte Whitner, Tashaun Gipson and the rest of the Cleveland secondary believe they can be the backbone of a tough Browns defense, it's been Hafley's job to make sure they aren't cutting any slack at all in practice.

"I have to make sure I'm hard on them," Hafley said. "Everyone keeps saying are we the best secondary? Is Tashaun the best safety? Is Joe the best corner? And my message to them was that each year, the best recommit themselves to new goals to being better than they were last year. Past success doesn't determine future success.

"We aren't going to compare ourselves to any other team anymore. We are just going to compare ourselves to us."

Hafley is glad his guys are being challenged like this in training camp. He gave credit to McCown for picking them apart in 7-on-7 drills, where the football rarely hits the ground.

"He keeps the ball moving forward," Hafley said. "He throws it to the open guy. You don't really see him make bad plays. He'll run the ball when nobody is open. If we keep the ball moving forward and he's throwing short completions and letting our guys make plays, he picks up blitzes and he sees things. Josh is into it, which is awesome to see."

McCown said his No. 1 focus during training camp is to master the offense, and he's been executing so far. What that does is firmly win over teammates, especially the ones on defense who endured tribulations watching the position from the sideline during the December losing streak a year ago.

Whitner was so impressed after Friday's practice, he posted a hat tip to the offense on his Twitter account, which reaches more than 157,000 people.

"Who's Donte going to give credit to?" Hafley said to laughing reporters. "He doesn't do that very much. If Donte is giving a guy credit? Shoot…"