The sideline has alway been called the "12th man" or "12th defender" in football, but like a rookie making a jump from his first to second year in the NFL, the sideline suddenly got beefed up overnight.

As part of the new "Crown of Helmet" rule implemented Wednesday at the NFL's owners meetings, the sideline is looking a whole friendlier to the defense and a whole lot scarier to the offense.

To be fair, the new rule addition applies equally to both offensive and defensive players. Neither can strike an opponent with the top of his helmet outside the tackle box, but the new rule is notable for its protection of defensive players after years of rules being instituted to protect those on offense.

As a safety that stood at 5' 8" during my playing days at the University of Technology-Sydney in Australia, tackling technique is a topic near to my heart. When taking on opposing ball carriers I rarely, if ever, had the advantage in size.

I learned very quickly that I had to win the leverage battle, bend at the knees and hips, hit low with my head up and take out an opponent's legs. If I didn't, I'd get bowled over.

The sideline was also my best friend. You learn to play angles when you're a safety and forcing ball carriers to the edges of the field helped to limit the options they'd have in the open field.

Safeties in the NFL are a whole lot bigger and faster than myself, and I can see how they'll be grinning when taking on a running back barreling down the sideline from here on out.

Running backs will have to be very wary about lowering their helmet as they prepare to be hit. If it's viewed that the running back is initiating contact with the helmet, they risk being flagged.

So what's a running back to do? They can run upright and absorb the contact, which isn't a very appealing option, or they can run out of bounds to avoid contact.

Think about when it's time for an offense to run its four-minute drill. Imagine that offense is up by a field goal late in the fourth quarter looking to run out the clock.

A running back takes the handoff for an off-tackle run. He bounces out toward the sidelines but necessarily has to stay in bounds to keep the clock ticking. He can't initiate contact, and he can't run out of bounds. Are we in the era of seeing a running back slide like a quarterback?

It's a slippery slope the NFL is traversing. And indeed, it's all about how the rule is enforced.

Former NFL general manager Charley Casserly said Wednesday on the NFL Network said he'd like to see referees penalize only flagrant instances of the new rule, err on the side of not throwing a flag and allow the NFL to dole out fines if necessary.

That's perhaps the common sense way of enforcing the new rule. But is that realistic to expect when referees will be making the rule a point of emphasis?

The NFL is in a Catch-22 situation. It wants to enact player safety initiatives, especially in light of concussion lawsuits being brought against the league, but it also can't let its sport lose the physicality that gained it popularity.