As for rules the rule has been this way for years. Any player sliding into second has to maintain a straight path to the bag and cannot get out of that path. They cannot go in with cleats up. They cannot slide past the bag. For example if the throw takes them to the right (putting the bag between the runner and fielder) and the guy slides past the bag then we have interference.
If the fielder is standing in front of the bag then he is fair game as long as the runner doesn't come in spikes high.