Serena didn't look to put that much muscle at all into the first racquet she threw and it is BADLY warped, obviously the new one in the bag she pulled out she slammed several times.
https://www.yahoo.com/sports/video/serena-breaks-unused-tennis-racket-033730705.html
https://www.yahoo.com/sports/video/serena-breaks-unused-tennis-racket-033730705.html