Complex sentence: When the game is ready for release, the publisher sends copies of the final version of the game to the ESRB, who reviews the game's packaging, and a random number of games they receive are play tested for more thorough review.
Split into simpler sentences: When the game is ready for release, the publisher sends copies of the final version of the game to the ESRB. The ESRB reviews the game's packaging, and a random number of games they receive are play tested for more thorough review.