Rajon Rondo has a torn ACL, and the NBA’s leader in assists is done for the season. This is a damaging blow to the Celtics, who are already below .500 (20-23 heading into Sunday’s game against Miami), and had hoped some offseason additions could push them toward one more run at the NBA Finals with an aging nucleus.

You can forget that. Not happening. Their 5-year run of success, powered by Rondo, Kevin Garnett, Paul Pierce and Ray Allen, is over. Let the rebuilding begin.

2007-2008: NBA Champions, defeated LA
2008-2009: Lost in Eastern Conference Semifinals (Orlando)
2009-2010: Lost in NBA Finals (LA)
2010-2011: Lost in Eastern Conference Semifinals (Miami)
2011-2012: Lost in Eastern Conference Finals (Miami)

The big question now becomes: Who do you build around? Paul Pierce has two years left on his deal, what trade value does he have? Would a contender looking for a clutch scorer be interested? I’m sure someone will float Pierce for Rudy Gay, which would be interesting. Kevin Garnett turns 37 in May. Jeff Green and Brandon Bass are clearly complimentary players.

So the answer has to be Rondo, right? He only turns 27 in February and for a player of his caliber, has perhaps the best contract in the NBA ($12 million next year, $13 million in 2014-2015). But he’s also the best trade piece they have, and – before this injury – could have fetched them someone like Dwight Howard in a sign-and-trade.

Now you’ve got a situation like Darrelle Revis is in with the Jets: Once-great team now rebuilding, and do they do it around the best player in the league at his position, or trade him and start over?