Brad Stevens has brought defense back to the Boston Celtics. After his first two seasons with team resulted in respectable, but otherwise unspectacular results on that end of the floor, the Celtics have become one of the league’s best defensive units.

Take a quick look at any defensive efficiency rankings and you’ll see Boston sitting in third place behind just San Antonio and Miami. That the latter two are near the top of the NBA isn’t very surprising. Tim Duncan is still going strong for the Spurs while the Heat’s Hassan Whiteside is sending back opponent’s shot attempts at a league-leading rate. Puruse the Celtics roster and you won’t find a defensive anchor anywhere on their roster. In fact one of their biggest offseason acquisitions -- David Lee -- has one of the worst defensive reputations in the league.

So how is Stevens doing this?

By marrying his personnel to a smart, well-executed approach -- something a lot easier said than done at any level of basketball.

One of the core staples of Boston’s scheme is redirecting the vast majority of all pick-and-rolls they face toward the sideline -- the same “Blue”/“Down”/”Ice” concept made famous by former Celtics assistant Tom Thibodeau. Because the pick-and-roll is so prevalent in today’s NBA, this type of approach on defense means Boston’s opponents can spend entire possessions without getting the ball near the paint.

Don’t let the result of that play fool you. While Orlando’s Aaron Gordon sinks a tough shot in the above clip, that is exactly the type of possession that NBA head coach could live with every time down the floor. The ball never even gets close to the paint, despite the Magic getting to a second pick-and-roll (which is typically a good thing for an offense), and Gordon is forced to jack up a long, contested 2.

This concept certainly plays a role in Boston’s success, but the key ingredients to successful defenses are relatively unspectacular. Outside of having the personnel equipped to do it, most elite defensive units rely strongly on great effort, excellent communication and precise execution of their schemes. Under Stevens, the Celtics possess all those things along with one more factor that seldom gets noticed: the avoidance of “over helping.”

Because the typical image of a top tier defense is a bunch of players flying around causing havoc and stonewalling opponents with otherworldly effort as they attempt to find good shots, a help defender not reacting to an offensive player's attack on the basket seems counterintuitive to the whole endeavor. But in the NBA, the discipline to maintain a good help position is just as important, if not more so, than the awareness and willingness to aid a teammate caught in a bad spot. Such logic is why more teams are trying to come up with defensive schemes to that require less players to be involved in stopping actions like the pick-and-roll.

Boston certainly qualifies as one of these teams. Just take a look at this possession in a recent game against San Antonio.

As you go through each part of that possession, Celtic help defenders aren’t sealing off options for Spurs because of manic, uncontrolled effort (also known as the college basketball approach to defense), but because they are in perfect positions to stamp out every threat until the ball ends up in Avery Bradley’s hands. The really impressive part is when San Antonio’s Leonard drives along the baseline -- the place Steve Nash used to pick apart defenses for years (because they over helped on his drives) -- and not a single Boston player got suckered into giving up an easy bucket.

The end result of that play is yet another reason why Boston has been so hard to score on this year: turnovers. As in the Celtics are the best in the league at forcing them. This probably isn’t too much of a shock when for a team that employs pitbulls like Jae Crowder, Avery Bradley and Marcus Smart. Overall, Boston has five players in the top 35 of steal percentage, per our own RealGM data, with Isaiah Thomas and Kelly Olynyk joining the aforementioned trio.

The inclusion of the latter two is a bit surprising given their perceptions as defensively liabilities. Due to his size, Thomas will always have some limitations, but in Stevens scheme he’s proven to be a real pest; constantly being a threat to poke the ball away from a careless ballhandler in pick-and-rolls or anticipating passes out them and generating deflections:

Olynyk’s defensive impact is the even bigger surprise. Since he came into the NBA, the perceived knock on Olynyk was always his ability to provide an impact on the defensive end of the floor. Perhaps because of the influence of Stevens, Olynyk has went from potential liability to positive force as Boston is a point and a half better -- 96.0 to 97.5 -- with him on the floor defensively, per NBA.com data. Olynyk’s underrated agility and quick hands have turned him into a menace in terms of generating steals and deflections both on and off the ball.

With so many ball hawks, it’s no wonder Stevens employs the defensive concepts he does in pick-and-roll. By pinning the ball to one side of the floor, Stevens can use the combination of great on-ball defense from players like Smart, Bradley and Crowder to force opposing ballhandlers to throw rushed, pressured passes toward a well positioned group of thieves.

Along with the Warriors, the Celtics are showing us that it doesn’t take intimidating rim protectors to build an elite defense. With a sound scheme, a focus on fundamentals and an enviable collection of perimeter defenders, this motley crew in Boston is in the thick of things in the Eastern Conference playoff race once again because of their ability to frustrate and turnover opponents on a nightly basis.