With NBA free agency opening Tuesday, we continue our annual examination of the options available to the Celtics  at each position. Today’s focus: Centers. Unlike recent seasons, C’s president of basketball operations Danny Ainge is expected to have more flexibility than any summer since 2007 when the league’s moratorium on free agent signings is lifted and the salary cap (an estimated $63.2 million) is officially set on July 10.
- 2014 NBA free agent point guards available to Celtics 
- 2014 NBA free agent shooting guards available to Celtics 
- 2014 NBA free agent small forwards available to Celtics 
- 2014 NBA free agent power forwards available to Celtics 
The Celtics  have eight players under guaranteed contracts in 2014-15 for $48.5 million (Rajon Rondo  $12.9M; Gerald Wallace  $10.1M; Jeff Green  $9.2M; Brandon Bass  $6.9M; Joel Anthony  $3.8M; Vitor Faverani $2.1M; Kelly Olynyk $2.1M; Jared Sullinger $1.4M) as well as $4.1 million in cap holds for first-round picks Marcus Smart and James Young. Pending decisions on or by Kris Humphries, Avery Bradley  and Jerryd Bayless, the C’s could have as much as $10 million in cap space — or more if they use the stretch provision on Wallace.
Considering Faverani and Anthony are the only true centers on the roster, the Celtics  should have every free agent 5 on their radar. Last year’s second-round pick, Colton Iverson, who played in Turkey this past season, is another option, but the C’s need a legitimate rim protector if they have any hope of making the playoffs this winter.
Without further ado, let’s take a look at their options, separating the current free agents into three categories.
THE ROBERT PARISH  HONORARIES
Not only are the C’s lacking a starting 5 of any note, we’re now going on Year 4 in the search to replace Kendrick Perkins  — and even he was more myth than Celtics legend. The current free agent crop, as usual, offers few realistic solutions in the paint, only stressing the importance of finding a rim protector at all costs.
RICH MAN: GREG MONROE
2013-14: 2,690 min, 15.2 ppg, 9.3 rpg, 2.1 apg, 1.1 spg, 53.1 TS%, 18.1 PER
Why? The 6-foot-11, 253-pound southpaw has been a reliable force in the middle since entering the league in 2010, playing all but three games in his career.
Why not? As sound as he’s been, Monroe’s not an All-Star. Still, in order to pry him from the Pistons, it would take a max deal, and Detroit still might match it.
COMMON MAN: MARCIN GORTAT
2013-14: 2,655 min, 13.2 ppg, 9.5 rpg, 1.7 apg, 1.5 bpg, 56.8 TS%, 17.6 PER
Why? The C’s interest in Gortat dates back to his days in Phoenix, and the Polish Hammer arguably enjoyed the best season of his career for the Wizards this past winter. The interest also appears to be me mutual .
Why not? The Wiz are intent on keeping Gortat, and he’ll also be linked to every team in need of a center (Miami?). Past his 30th birthday, he made $7.7 million last season and should make even more this winter.
POOR MAN: SPENCER HAWES 
2013-14: 2,470 min, 13.2 ppg, 8.3 rpg, 3.0 apg, 1.2 bpg, 55.4 TS%, 15.7 PER
Why? Hawes shot 41.6 percent on 308 3-point attempts for the 76ers and Cavaliers  in 2013-14, bringing a floor spreading element that Celtics coach Brad Stevens  covets. The 7-footer also had his best year on the boards.
Why not? If it’s rim protection you seek, Hawes isn’t exactly Shaquille O’Neal  in the paint. While he brings an attractive offensive element, he’s a big body who doesn’t exactly play like one opposite physical centers.
HOMELESS MEN: Channing Frye  (2,312 min, 11.1 ppg, 5.1 rpg, 1.2 apg, 55.5 TS%, 13.2 PER); Chris Andersen (1,396 min, 6.6 ppg, 5.3 rpg, 1.3 bpg, 68.3 TS%, 18.5 PER); Jermaine O’Neal (883 min, 7.9 ppg, 5.5 rpg, 57.0 TS%, 15.3 PER); Chris Kaman  (736 min, 10.4 ppg, 5.9 rpg, 1.5 apg, 1.0 bpg); Emeka Okafor  (2,052 min, 9.7 ppg, 8.8 rpg, 1.2 apg, 1.0 bpg, 49.6 TS%, 15.8 PER).
THE JOEL ANTHONYS
If finding a starting center is so difficult, just imagine how hard it is to find a legitimate backup. Hence, Anthony’s $3.8 million salary. The Celtics have spent the past several seasons forcing natural 4’s into the 5 spot, but perhaps they’d be better suited investing in a less expensive 7-footer, whatever the risk.
RICH MAN: ANDREW BYNUM 
2013-14: 516 min, 8.7 ppg, 5.6 rpg, 1.1 apg, 1.1 bpg, 45.6 TS%, 15.2 PER
Why? There’s a reason the Cavaliers and Pacers have taken a risk on Bynum despite his apparent apathy: He’s a 26-year-old who once averaged 19 and 12.
Why not? He missed an entire season in Philly (knee), got traded from Cleveland (immaturity) and sat out Indiana’s final 11 games (knee). Need we say more?
COMMON MAN: GREG STIEMSMA 
2013-14: 1,007 min, 2.9 ppg, 4.1 rpg, 1.0 bpg, 58.4 TS%, 9.7 PER
Why? After his surprising run with the Celtics in 2011-12, Ainge would have gladly brought the 7-foot shot blocker back for another season had the Timberwolves  not offered a contract the C’s couldn’t possibly match.
Why not? Even in Boston, Stiemsma battled nagging injuries, and a strained MCL cost him 27 games for the Pelicans this season. He’s been waived by Minnesota and New Orleans in the span of nine months.
POOR MAN: GREG ODEN 
2013-14: 212 min, 2.9 ppg, 2.3 rpg, 56.7 TS%, 12.4 PER
Why? In much the same way teams still hand over millions to Bynum, it’s hard not to hold out hope the former No. 1 overall pick will reach his potential if he can stay on the floor. And he’s still only 26.
Why not? The 7-footer spent three seasons sitting with a series of knee injuries, and he averaged just 9.2 minutes over 23 appearances for a Heat team that desperately could’ve used a healthy Oden’s services this past season.
HOMELESS MEN: Gustavo Ayon (429 min, 4.3 ppg, 4.8 rpg, 1.1 apg, 1.0 spg, 50.5 TS%, 12.9 PER); Lavoy Allen  (1,072 min, 4.7 ppg, 4.8 rpg, 1.1 apg, 47.0 TS%, 12.5 PER).
THE VITOR FAVERANIS
Either not worth the asking price or not worth any price, these guys are a dime a dozen and wouldn’t be an upgrade over Faverani or any available center at the league minimum. Thanks, but no thanks.
Cole Aldrich: 330 min, 2.0 ppg, 2.8 rpg, 62.0 TS%, 19.1 PER
Aron Baynes: 491 min, 3.0 ppg, 2.7 rpg, 46.7 TS%, 9.7 PER
Andris Biedrins: 45 min, 0.5 ppg, 2.8 rpg, 41.2 TS%, 2.4 PER
Marcus Camby : 250 min, 1.8 ppg, 3.3 rpg, 34.2 TS%, 8.6 PER
Jason Collins : 172 min, 1.1 ppg, 0.9 rpg, 48.5 TS%, 4.1 PER
Aaron Gray: 355 min, 1.8 ppg, 3.0 rpg, 46.6 TS%, 7.8 PER
Ryan Hollins : 482 min, 2.3 ppg, 1.5 rpg, 73.0 TS%, 11.9 PER
Bernard James: 146 min, 0.9 ppg, 1.4 rpg, 50.3 TS%, 8.5 PER
Nazr Mohammed: 562 min, 1.6 ppg, 2.2 rpg, 44.5 TS%, 10.1 PER
The Celtics simply cannot enter this season with Faverani, Anthony and Iverson manning the middle and have any chance of emerging from the lottery. Obviously, Monroe would be the ideal scenario, but Ainge would have to work a bit of salary cap magic in order to free up enough space to offer him a max contract. And even then the Pistons could match their offer. Gortat and Hawes are also intriguing options, although they’ll have plenty of suitors, too.
In short, the available rim protectors are few and far between, illustrating why the Celtics would have assumed the risk in drafting Joel Embiid had he fallen to sixth in the draft order. Are Bynum and Oden worth the risk? Quite possibly. Otherwise, you’re looking at a 31-year-old Okafor or the return of the Stiemboat as potential upgrades.