He was arrested for assault with injury on his girlfriend, he made bail and then drove his Cadillac SUV off a cliff. He is currently being treated at a hospital.
It's looking like the crash was caused by his falling asleep at the wheel. I read the article in the local paper, the North County Times, and it looks like he missed a right turn and drove straight onto the beach in Carlsbad on the way home from a long night in booking and the county slammer. I'm pretty familiar with the spot, having lived about a mile north of Seau's home in Oceanside for three years in the late 90s. He's a genuinely good dude. Sounds like his latest piece of ass just got a little too sassy.