The 10th NHL game has long been a milestone of sorts for young players looking to break into the league, especially teenagers. That's because it's an indication of whether the player is ready to play at the sport's highest level or if he needs more time to develop. A team that thinks the player needs more time to develop will often decide to send the player back to his junior team before that 10th game, preserving the first year of the player's entry-level contract (ELC) for another season.
Ultimately, if the Bruins are middling and aren't staring at a potential playoff run, Boston likely wouldn't have to worry about burning Hagens' first year of team control. An 18/19-year-old player can avoid burning the first year of his entry-level deal by playing 10 or fewer games in his first pro season - allowing that contract to slide forward a year. So, if the Bruins are closing out the year without a playoff berth and Hagens is ready to go pro in late March/early April, Boston could give him 8-10 games to dip his toe in the water without worrying about his contract.