Coming into the season, much of the Celtics’ concern was on the defensive side of the ball and those fears were well founded. This was a team that, after all, lost arguably their two most important defensive anchors in the front court and seemed to have a real lack of rim protection. With Al Horford going off to Philadelphia and Aron Baynes shipped to Phoenix, Boston started the season down two of the main reasons why they finished with the first and seventh best defenses in the two previous seasons.
But now, here in March and nearly 60 games in, it’s clear that those qualms were wildly misguided as this Celtics team has not skipped a beat on defense. After allowing 107.9 points per 100 possessions last year per Cleaning the Glass, the C’s are giving up just 106.3 points per 100 possessions this year, good for fourth in the league. So how exactly has the team managed to improve on defense despite losing two crucial big men? Well, one big reason has been the team’s defensive versatility and ability to switch.
Horford and Baynes’ departures left a gaping hole in the middle of the floor which Daniel Theis happily strolled into, but it also meant that at least one of the Celtics’ starting trio of wings would have to consistently guard power forwards on a nightly basis. While each of Jaylen Brown, Jayosn Tatum, and Gordon Hayward are around the same height in that 6-6 to 6-8 region, Brown is by far the heaviest at 223 pounds and, so far this season at least, has been the one often tasked with guarding the bigger players. This chart from Krishna Narsu’s versatility app does a great job of showing that shift in defensive role for Brown.
The chart plots the time Brown has spent covering guards and forwards over the course of his career, and as we can see, there has been a huge shift in his defensive role compared to what it’s been over the past two seasons. With Baynes and Horford on the roster, Brown spent most of his time chasing guards – around 60% over each of the past two seasons. This year, though, with those two gone, Brown has been tasked with dealing with bigger players and splits his time almost evenly between matching up against guards and forwards. As he showed in the late February matchup against LeBron James, Anthony Davis, and the Lakers, Brown is more than capable of holding his own against bigger players.
And while it’s Brown who’s usually the one that guards a position up with the starters, this Celtics team is full of versatile defenders capable of switching everything. Tatum, Brown, and Hayward are just about as interchangeable as it gets in the starting lineup but, even coming off the bench, the Celtics are full of capable, switchy wings in (when he’s not starting) Marcus Smart, Romeo Langford, and Semi Ojeleye. All six of those players are not only solid defenders, but can also guard multiple positions.
A quote from Brad Stevens back in 2016 after the Celtics drafted Jaylen Brown, is pretty illuminating in terms what kind of player he wants defensively. At Brown’s introductory press conference, Stevens said “the more versatile, the more positionless, the better.” Now, he finally has the personnel to execute on that vision. In terms of team versatility – which is a weighted average of individual versatility that can be considered a measure of how switchy a team is – the Celtics rank third in the entire league, trailing only the Rockets and the Raptors.
One of the drawbacks with switching are mismatches, but the sheer adaptability of the Celtics’ wings means that those opportunities are hard to come by for opponents. Take this pick-and-roll action from last week’s Lakers game with LeBron James and Anthony Davis working on Tatum and Brown.
The Lakers get the switch they want with Tatum guarding Davis and set up the big man in the post, but Tatum is ready for Davis’ spin move, and manages to strip the former Kentucky Wildcat, eventually forcing a jump ball.
Switching almost everything means that, when the game slows down, the opponent can often choose – and exploit – the matchups that they want. As such, it requires high levels of trust – not just from player to player, but from coach to player, too. Brad has to trust all five defenders out on the court because he knows that at any given time, they could be on any one of the offensive players. It leaves situations like this, where Romeo Langford is left alone on an island with James Harden.
Many other coaches would have called for a double to help out a rookie going against the best offensive player in today’s game, but Langford has earned his coach’s trust with his defensive play and proved Stevens right by getting the stop and forcing a brick.
Even Daniel Theis has shown an impressive ability to stick with guards on the perimeter. On a crucial possession in overtime against the Houston Rockets, Theis was matched up with Russell Westbrook just inside the arc, and did a great job to force a tough, contested mid-range jumper on such a big possession. He showed this ability back in January, too, with a game-winning block on Trae Young. Teams will look to take advantage of Theis’ switching in the playoffs, but if he can hold his own out on the perimeter, it will be a big boost to this Boston defense.
Of course, switching is much easier on the defensive end with Kemba Walker on the bench, as the Celtics were against the Rockets, but even with Walker in the lineup the Celtics switch as much as possible. The only difference is, if Walker is switched on to a big, Boston has to scramble him out of the post with another player. Below, we see Walker matched up on the block against the much bigger Danilo Gallinari. After tussling with the Italian for position, Walker gets help from Grant Williams and the two manage a seamless switch back and even force a turnover.
Perhaps the biggest value of switching comes with its ability to limit pick-and-roll play, as it negates the value of the screen. As a result, this kind of defense forces a lot of isolation plays, making the Rockets, an iso-heavy team with one of the most dominant isolation scorers in the history of the game, one of the Celtics’ worst matchups defensively. While they didn’t manage to get the win on Saturday night, the Celtics’ ability to switch on defense is one of the main reasons behind their fourth-ranked defense and will be incredibly helpful come playoff time.