ROSEMONT, Ill. – Aggression makes for a champion – sort of.

As one of the basic principles in judging boxing, being an aggressive fighter can help anyone’s chances of winning a fight. However, this may not apply to Fernando Vargas.

In his last two bouts, he’s tucked his left arm over his stomach, pinned his chin to his chest and pillowed the right side of his face with his other glove. He’s bobbed and weaved. He’s ducked and sidestepped.

For anyone who has ever tried to hit Floyd Mayweather Jr., this stance is familiar and frustrating.

Vargas applied it against Raymond Joval. The tactic had Joval connecting very little of what he threw and Vargas landing all of what little he tossed at Joval.

It was clean. It was boring. But it was nonetheless effective in earning Vargas a victory.

Chicago is a city that has lost its reputation as a boxing capital to the casino-fed towns of Atlantic City and Las Vegas. But the Windy City knows what it likes, and that’s an explosive fighter.

I had hoped Vargas might have picked up his game a little more for the two-time middleweight champ Castillejo. Having seen two weekends of boxing in Chicago and how the crowd turned against stick-and-move fights, Vargas’ shell might keep Castillejo’s hands from reaching delicate tissue, but it wouldn’t shield him from the shower of disdain radiating from a crowd craving action.

One could easily tell the Allstate Arena crowd wanted hard, fast action after Humberto Soto nearly smothered Rocky Juarez with leather in their WBC interim lightweight title bout. It was the only 12-rounder of the evening.

Vargas originally signed to fight Castillejo for his WBC super welterweight belt in another 12-rounder. But Castillejo was stripped for not facing the man the commission had deemed the mandatory challenger: Ricardo Mayorga.

If Castillejo didn’t want to face Mayorga, the commission would set it up so someone would face him. So what if Mayorga had only recently righted himself after Felix Trinidad and Cory Spinks had put him away? I know: It’s wrong, unethical and represents everything that’s wrong with boxing.

Meanwhile, Vargas took on a boxer who had his title stripped by a hard-line policy, not by a hard right cross. It made Castillejo dangerous and, by losing his belt in such an unconventional way, still a champion.

Vargas attacked in the first three rounds, firing 1-2 combinations to Castillejo’s head. The shots Vargas delivered to the Spaniard’s body left it noticeably red. It was only a matter of time until that 1-2 strike wobbled Castillejo enough to open him up to a double-tap left hook that dropped him in the third round.

This proved a remarkable improvement over his bout with Joval. The crowd embraced the activity, but only for as long as he could keep it up.

The fight progressed and Vargas started to wilt. He pulled back into the shell that deflected so much of Joval. He started ducking, weaving, bobbing and sidestepping Castillejo.

Unlike the less talented Joval, Castillejo’s experience came through as he kept Vargas on the defensive with plenty of punches, although none of them seemed to be of a devastating magnitude.

But almost suddenly, a simple jab hit Vargas and he staggered. His mitts came to life, but lacked the precision he’d worked so hard to maintain.

Vargas doubtless won the bout by virtue of knockdown, but showed that at 27 years old, he’s not the same fighter that captivated the world when he won his first world title less than a decade ago.

To his credit, he didn’t go down. But he’d been damaged enough by the beating that his left cheek had swollen like a hamster’s packed with food. He just couldn’t move fast enough to avoid Castillejo’s advances.

“We hope it’s not a broken jaw,” manager Shelly Finkel said of Vargas’ bulbous cheek.

It seemed to swell even after the fight during the press conference. One of Vargas’ seconds held a towel full of ice to his cheek, which led to a more impeded speech.

Even before he stepped to the podium, all eyes were on Vargas. He’d won the fight, but the decision was shockingly lopsided in his favor. It was a bitter mood, in which all scrutiny was ironically trained on Vargas.

He hadn’t lost the fight, but the questions were waiting for him. Answers were needed for why the fighter who goes by “Ferocious” didn’t resemble much of the word.

“I felt a little off because of the undisclosed amount of weight I lost, but we won’t talk about that,” he said.

There’s a humorous element to recalling that Castillejo showed up a pound overweight at the weigh-in. He had to strip beyond undergarments in public to shave that extra pound. It worked.

It made the thought of Vargas’ weight-loss woes all the more interesting.

“I’m at the point in my life where I’m telling myself I’m not doing that do my body no more,” he said. “I’m 27 and you can’t be going up and down like that because your body ain’t gonna go with you next time.

“The more you keep doing it to your body, the more your body fights.”

At least some part of Fernando Vargas was fighting up to that point.

He confided that he’d like to stay around 170 or 175 pounds on the street. It’s not an unreasonable amount, but it makes one wonder how much weight he carried around before this fight. Enough weight to make him “sluggish,” Vargas said.

“You don’t know the world I can introduce you to if I stick close,” he added.

For the sake of Vargas’ career, the world he has in mind won’t resemble the one he’s acquainted us to this year.