ALLEN PARK — Aaron Brown, the Lions’ back-flipping rookie running back, took a hit this morning that was heard across the field and maybe across the Southfield freeway too.
 After catching a pass from Daunte Culpepper, he was blindsided by rookie safety Louis Delmas with a bone-rattling, open-field tackle in what was the biggest hit of training camp so far.
  Coach Jim Schwartz said Delmas crossed the line.
  “When a guy is not expecting it and is in a vulnerable position, he was motoring to get there, I appreciate the effort but  we need to be smarter about that,’’ Schwartz said.
   Gunther Cunningham, the defensive coordinator, looked at it a little differently.
 “We’ve really been working hard to become a physical team. Having Louis Delmas back out — he shouldn’t do that in practice — but I turned around and smiled. I loved every second of it, boy he blew him up. That’s the kind of tackling we’re trying to get out of him,’’ Cunningham said.
   Brown, who was not hurt, and Delmas were smiling about it afterward.
   Delmas missed a week and a half of camp with a bum knee. Today was his first practice back in full pads.
— PAULA PASCHE