The Boston Celtics entered free agency quietly with a two-year, $24 million deal with Amir Johnson.

Johnson, who has split his NBA career between the Detroit Pistons and Toronto Raptors, has the distinction of being the last player to jump from high school straight to the pros. Detroit drafted him 56th overall back in 2005. His lack of college experience makes him a 28-year-old with 10 years of experience.

The knock on Johnson throughout his career has been that he’s perpetually dinged up and has never carried a heavy minutes burden. Durability issues have been overblown -- he’s missed just 25 games since 2009 – and Brad Stevens is unlikely to ask him to play starter minutes with Jared Sullinger and Kelly Olynyk still on the roster.

Johnson earned $7 million from the Raptors last season. This deal represents a $5 million raise after a season in which he averaged 9.3 points, 6.1 rebounds and 0.8 blocks. That might elicit a very negative knee-jerk reaction, but most advanced statistics have been kind to Johnson and the Boston Herald reports the second year of the contract is non-guaranteed. That gives Danny Ainge significant flexibility as teams prepare for an undetermined increase in the salary cap for the 2016-17 season.

The popular calculation being used to put this month’s contract agreements into terms we are familiar with is to trim a third of the value off the top. If you have a problem giving Johnson $12 million, then you can consider his deal to be roughly $8 million in the NBA’s most recent market. Johnson assumes the distinction of becoming Boston’s highest-played player, but if Ainge has his way that won’t be the case for long. Ainge is still holding plenty of assets to pull off a significant trade and at least Johnson should get significant run. The team’s second highest-paid player, Gerald Wallace, has been a glorified assistant coach.

Grade for Johnson: A-

Johnson’s greatest impact on the Celtics will come on the defensive end. Brad Stevens had Boston playing good defense despite the lack of a true rim protector last season. His defensive skill set is much more varied than that of Sullinger, Olynyk or Tyler Zeller. He’s also a better defender than Brandon Bass, who is also a free agent.

Over his career Johnson has 3.8 block percentage; although that figure dipped to 3.3 during his six seasons with Toronto. No player that logged more than eight games for the Celtics had a block percentage higher than 2.8 last season. That player was Gigi Datome. Johnson will immediately become one of Boston’s better rebounders. The Celtics ranked 15th in defensive rebounding and 17th in offensive rebounding last season.

Johnson also rates favorable in terms of ESPN’s real plus-minus (1.81) and WAR (5.07), which ranked 70th in the league.

Grade for Celtics: C+

It’s not a bad signing, but it’s not a satisfying one either. Not after months and months of asset accumulation that have left the Celtics with only Amir Johnson to show for it so far. The Celtics continue to acquire nice role players without a franchise defining player.

There is also concern that Johnson’s rim protection will become average (or below average) as he ages and loses his athleticism.

According to Nylon Calculus, Johnson may already be showing signs of slipping defensively.  After allowing opponents to shoot 47.9% at the rim in 13-14 (slightly above-average), that figure jumped to 55.2% last season. Believe it or not, Zeller (53.3%) actually rated better.

Offensively, Johnson isn’t going to stretch the floor. An overwhelming majority (84%) of his shots came from within 10 feet, including 48.9% at the rim. He has shown an ability to executive in the pick-and-roll and might prove to be a nice tandem with Isaiah Thomas/Marcus Smart in that capacity.