Laravel eloquent - get the most recent row when using WhereIn function

I currently have a function:

Score::whereIn('site_id', $sites)
      ->where('type', 1)
      ->avg('score');

But at the moment, as you can see, it averages out amongst all results within the Scores table. I want to only average out against the most recent row of each $site_id (the table may not have all $site_id's in the results though).

The table has a created_at column, which will determine which is the latest one by date/time.

Thank you for your help.

via Chebli Mohamed