It is interference by a batter or a runner when --
(d) Any batter or runner who has just been put out hinders or impedes any following play being made on a runner. Such runner shall be declared out for the interference of his teammate;
Rule 7.09(d) Comment: If the batter or a runner continues to advance after he has been put out, he shall not by that act alone be considered as confusing, hindering or impeding the fielders.
Based on the letter of the rule, even the traditional "clean slide" to break up the DP can be called as interference. In the play in question today, however, it was not a traditional "clean slide," it was a clean slide combined with the runner attempting to grab the fielder's leg. The interference call was technically correct and more or less in keeping with tradition as well. [Jay]