It turns out that the second season of Overwatch Competitive Play didn't work out quite as Blizzard had envisioned. "When Season 2 started, we had WAY more players in Gold and Platinum than we initially intended, and way fewer in Bronze and Silver," designer Scott Mercer explained in a recent forum post. "This was the result of how we calculated your initial SR for Season 2. We tried to partially reset player SR at the start of Season 2, but the results were not as we expected."
What ended up happening was that "below-average players" began season two with a higher skill rating than they should have had, which then declined as the season progressed. That "didn't feel great," Mercer said. "It also meant that there was a much wider variation of skill in the Gold and Platinum tiers than we wanted."
To avoid that in season three, Blizzard is changing how it determines starting skill ratings, and will focus more on "trying to keep things fair rather than giving everyone a fresh start." Initial skill ratings will run slightly slightly lower this time around, to ensure that fewer players see drastic declines. The potential downside to the adjustment is that some players won't start in the same tier for season three as they did in season two, and SR gains will be a little more pronounced at the beginning of the season, although they'll eventually smooth out. But "fewer players should start the season having their skill rating drastically drop despite having close to even wins and losses," Mercer said.
The new system is currently in testing on the PTR, and Mercer warned that further adjustments "might require a reset of placement matches" to ensure that everything is ticking away as it should. "If that’s the case, we’ll try to provide advanced notice whenever possible," he said. He also announced that, "based on community feedback," the off-season period between seasons two and three will be shortened to just one week. That means the third season of Overwatch Competitive Play will begin at 8 pm ET/5pm PT on December 1.