Bear with me here, as there are several definitions and opinions of what "bad" is. To me, a bad coach is one who fails to adapt, to utilize his team's strengths, and too often plays into the opponent's system. Thanks to some quick research from patrit19, we have established that Colorado's record against their division under Sacco is as follows:
1st year: 10-11-3
2nd year: 7-16-1
3rd year: 2-12-1 (so far)
For a total of 19-39-5 (thanks Mike). Abysmal would be insulting to the word abysmal.
Why it means he's a bad coach: Other than the obvious (under .500), this is hard evidence of what many of us fans have speculated for a while now: He fails to adapt. The teams that know the Avs best (their division) have no problem beating them--and it's become worse and worse in each season, as teams become more and more familiar with the Avalanche style of play. Eastern teams? No clue how the Avs play--and the Avs eat them up.
It's time for Sacco to go. Will the Avs get someone better? Who knows. But at least for a while, maybe the division won't know exactly how to handle the Avs.