For me it's Marcus and Jae. Defense and effort plays mean so much for a team that's low on talent, and these two guys are the spark for both units
I agree 100%
I don't think you can really measure (with simple stats) just how much impact Smart and Crowder have had on this team's recent success...and I'll throw Bradley in there too.
Three key things that have driven this great run:
1) A dramatically improved defence
2) One of the lowest turnover rates in the league
3) Winning hustle plays
Smart, Bradley and Crowder have been key guys in achieving that.
Rondo is very talented, but he was also a turnover machine and rarely finishes a game with less than 4 turnovers. Smart and Bradley usually finish with 3 or less
combined.
Smart obviously hasn't passed the ball like Rondo, but his assist-per-turnover ratio has been phenomenal, especially for such a young guy in his rookie season.
With Avery + Smart in the game you have arguably the best defensive backcourt in the NBA, and yet those two guys also have among the lowest turnover rates in the game for guys who play as many minutes as they do.
Keeping turnovers down means less easy transition layups/dunks for the opposition, and when you combine that with stifling half-court defence it makes this team very tough for opponents to score against this Celtics team...and as we all know, any time you play great defence you're giving yourself a chance to win.
When we have Smart/Bradley/Crowder/Bass/Zeller on the court it's hard to imagine many NBA defences being better than that.