NFHS bags has to be secured so there is no movable base rule.8-8-14 is your closest bet, the base if dislodged is considered to follow the runner and the runner is protected unless they try to advance. So unless something else about the slide other than going farther than normal that is illegal occurs, or judge that the runner intentionally interferes,its legal.
Best way to judge if they tried to take out the fielder behind is if they hit the dirt within 2 foot or so of the bag. Go to a field where there are fixed bags and after a game, you'll see the slide marks in the dirt starting at least 4 feet from the bag.
Rule 8-8-14 NFHS SB Runner is not out:
The runner slides into a base and dislodges it from its proper position. The base is considered to have followed the runner.