PHOENIX - It was a "tough year" for NFL commissioner Roger Goodell, whose performance has come under scrutiny despite the league's soaring popularity. The 2014 season included domestic violence problems; a child-abuse case involving one of the league's best players; officiating controversies; and a league investigation into one of the participants in Sunday's Super Bowl.

Goodell's annual state of the NFL news conference Friday capped a season that invited more criticism than celebration for the commissioner.

"Listen, it has been a tough year," Goodell said. "It's been a tough year on me personally. It's been a year of what I would say is humility and learning. We, obviously, as an organization, have gone through adversity. More importantly, it's been adversity for me. We take that seriously. It's an opportunity for us to get better."

Goodell said the season prompted "soul searching."

Regarding domestic violence, he said the league did not have a policy in August and has since worked with experts and advisers to help the league understand how to proceed. He said the league's new personal conduct policy is a sign of improvement.

"We, as the NFL, and this commissioner understand it a lot better today than we did before," Goodell said. "I think we in the NFL want to make this an important issue where we can make a difference in society in general. This is a problem in the broader society."

The issue that has garnered considerable attention is the investigation into the air pressure of the footballs in the AFC championship game, when 11 of the 12 balls that the New England Patriots used were below the league's mandated levels.

Goodell said the investigation, overseen by attorney Ted Wells, will focus on two questions: Why were the footballs not in compliance with the rules, and was the deflation the result of deliberate action?

"We don't know enough in this investigation to know who is responsible or whether there was even an infraction," Goodell said. "When we get the facts from Ted Wells, we will certainly take all of that into account, and we will make the right decision to protect the integrity of the league."

Seattle Seahawks cornerback Richard Sherman did not expect the Patriots to be disciplined because of the "conflict of interest" that comes from Goodell's relationship with Patriots owner Robert Kraft. Sherman cited a photo of Kraft and Goodell together on the night before the AFC championship game.

Goodell said that he attended a party as part of his responsibilities as commissioner, and that such a situation was not unusual.

On Monday, Kraft insisted the Patriots did not break any rules and he demanded an apology if the investigation vindicates the Patriots. Goodell did not sound as if he would be offering one.

"This is my responsibility - to protect the integrity of the game," Goodell said.

Seattle running back Marshawn Lynch has been reluctanct to participate in league-mandated media sessions, but Goodell was unforgiving, calling the requirement an "obligation that comes with the job and playing in the Super Bowl."

In his opening statement, Goodell said that the league was looking at ways to enhance replay and officiating, including reviewing penalties. The league is discussing rotating members off officiating crews in-season to "improve consistency."

The league has considered expanding the postseason - an extra playoff berth would have made the Eagles eligible this season - but Goodell does not want to dilute the regular season or conflict with college football.

Goodell also said the NFL was "aggressively pursing" streaming a regular-season game online. The game would still be broadcast in local markets, but it would be available for fans without traditional television service.

Those are all in discussion, but the best way to enhance the NFL might be to first restore faith in the league and Goodell after all the turmoil of 2014.

"We've already begun that process," Goodell said. "We have already begun the process of adding additional resources in terms of individuals that can bring an expertise to our office, an expertise to investigations."