* Doping tests, hard tackles sticking points
* Goodell expects HGH testing next season
* He wants players banned for repeat hits to head
More than a year after the National Football League (NFL) and the players' union (NFLPA) reached an agreement to end their bitter labor dispute, deep divisions remain.
They are especially at odds over the introduction of tougher doping tests and penalties for violent actions by players.
In the lead-up to Sunday's Super Bowl, both sides used their annual state of the game's addresses to point the finger of blame at each other for the failure to implement changes they promised when they signed a 10-year collective bargaining agreement in 2011.
On Thursday, the NFLPA laid out a series of complaints the union had about the league's approach to player safety and threatened legal action.
On Friday, it was the NFL's turn. What started out as a mostly positive address from commissioner Roger Goodell, quickly turned into a thinly-veiled criticism of the union's position.
"What I think disappoints me is that we reached a very comprehensive agreement a couple of years ago for 10 years to take the game to another level, and unfortunately we're spending most of our time focusing on issues that we had agreed to," Goodell told a packed news conference.
"I understand we're going to have differences, I understand why there are grievances, I understand why there are lawyers, but we have to find solutions for the best interests of the game."
Both sides said the protection of players was their top priority and acknowledged that changes needed to be made but they agree on little else.
Goodell said there was at least some hope that one of the prickly issues, testing for human growth hormone (HGH), may soon be resolved. The sides agreed in 2011 to introduce blood tests for HGH but that has still not happened.
NFLPA executive director DeMaurice Smith said on Thursday the union was concerned about the arbitration process that would be used if the test were approved but Goodell was more upbeat a day later.
"I believe that HGH testing is going to happen prior to the 2013 NFL season. It's the right thing to do for the players, for their health and well-being long-term," Goodell said.
"It's the right thing to do for the integrity of the game. It's also the right thing to do to send the right message to everybody else in sports.
"You don't have to play the game by taking performance-enhancing drugs. The science is there. There is no question about that."
The two sides also remain at odds over how to deal with on-field player safety issues, although there is shared recognition on many issues.
One is the need to clamp down on dangerous tackles, especially low blocks and hits to the head that can cause concussion.
Goodell said players were leading with their heads more than they used to, partly because modern helmets are better and players feel safer using their heads, but the medical evidence and rate of brain injuries did not support that.
"You can come up with a lot of theories that we've discussed but the reality is we have to get back to tackling, using the shoulders, using your arms properly to tackle," he said.
"And there is a strike zone, and that's where we are encouraging our players to focus and our coaches to coach that way, and it's made a difference."
But again, the sides differ over how to enforce any new role changes. Last season, the NFL suspended Baltimore Ravens safety Ed Reed for one game without pay for a late head-to-head hit, his third violation in three years.
But Reed appealed and succeeded in having the ban lifted and the penalty reduced to $50,000, about one-ninth of his game fee.
Goodell said the league was determined to press ahead with banning players who repeatedly breach the rules.
"Suspension gets through to them. It gets through on the basis that they don't want to let their teammates down, and they want to be on the field," he said.
"We're going to continue to emphasize the importance of following those rules. When there are violations, we will escalate the discipline."