What's it mean to videotape an football team walkthrough?

There’s an Associated Press story that uses this expression but I don’t think explains what in the world it means. Apparently it has something to do with spying on other teams in an unethical way. I don’t even know what a walkthrough is.

“By HOWARD ULMAN, AP Sports Writer
FOXBOROUGH, Mass. (AP)—New England Patriots owner Robert Kraft complimented the Boston Herald on Wednesday for apologizing for a story that said his team videotaped a St. Louis Rams walkthrough before the 2002 Super Bowl.”