Is there a semi-passive fund that just responds to the announcements that something is going into or out of an index? Presumably they'd leave a little money on

Is there a semi-passive fund that just responds to the announcements that something is going into or out of an index? Presumably they'd leave a little money on the table because they'd have to guess how much to buy in or sell out, but it'd probably mitigate a good chunk of the loss, right?