The Post Sports Live crew debates whether Stephen Strasburg’s recent pitching struggles are all in his head. (Post Sports Live)

We know Stephen Strasburg can be a stubborn, hard-nosed competitor. We saw it last season when the Washington Nationals insisted on shutting him down early and Strasburg tried every trick in the book to avoid it. He was mentally tough when he was fighting to save his spot in the rotation and play in the postseason.

So where was that guy Saturday after Ryan Zimmerman’s throwing error in an eventual loss to the Cubs? Because the guy we saw couldn’t shake it off, showed his general disgust to everyone in the ballpark, then walked a guy hitting below the Mendoza line, gave up a two-run double to pitcher Edwin Jackson, walked David DeJesus, allowed a single to Starlin Castro and a two-run single to Anthony Rizzo. Last season, the bull-headed Strasburg simply gets the next batter out, inning over. This season, he gives up four runs (albeit unearned).

Zimmerman is not himself this season. But his throwing error put a runner on first base. The rest of that mess could have been stopped by Strasburg, by not walking the immortal Darwin Barney, by not allowing the opposing pitcher to drive in two runs. And so on. Instead, he came unglued.

This can’t be tied to his Tommy John surgery. He came back from that last season strong, mentally and physically. He has been a salty, sometimes sullen competitor since he arrived in D.C. Where is that guy? Because the Nationals need him. They’ve managed to stay in the NL East race despite just one win from their putative ace, although we all know the ace is now Jordan Zimmermann. If the Nats made the playoffs and they began tomorrow, Zimmermann would be your first starter.

There is no question Strasburg has had some bad luck this season. A cursory count of errors turns up seven committed while Strasburg was pitching, including two by Zimmerman in that Cubs game. There is no question that the Nats’ fielding has been bordering on dreadful: They’ve committed 31 errors and are among the worst in the league in nearly all fielding categories.

But let’s look at those errors in Strasburg’s starts. The first was in his second start (6-3 loss to the Reds), committed by Chad Tracy (filling in for Adam LaRoche at first) in the third inning. It led to no runs. The Nats gave Strasburg three runs — not a bushel, but enough for a No. 1 starter. However, that No. 1 starter had given up three runs in the bottom of the first, all earned. I don’t recall his teammates pacing around the field, shaking their heads and muttering over his inability to get an out.

In his third start (a 3-1 loss to the Braves), Zimmerman committed an error that led to two unearned runs, and that was enough. Tim Hudson put the clamps on the Nats, allowing four hits. No doubt that was frustrating for Strasburg.

In his fourth start, he faced Mets phenom Matt Harvey, who held the Nats to one run. Shortstop Ian Desmond committed an error in the first inning and two runs eventually scored, but one of those came home on a wild pitch. Physician, heal thyself.

In his next start, Strasburg again gave up three runs to the Cardinals in the first inning. Rookie Anthony Rendon committed an error at third, but only after Strasburg’s day began this way: double, strikeout, single, walk, two-run single. All three runs in the inning were earned.

The Nats committed no errors in his next start, and Strasburg gave up only one run in the first inning; the Nats gave him two in the top of the second. This was one of Strasburg’s hard-luck nights: Tyler Clippard took the loss in relief.

In the start before the Cubs fiasco, Strasburg finally got the first inning back under control and while there was one error during his outing, on catcher Wilson Ramos, it led to no runs. Strasburg gave up four runs to the Pirates in seven innings, but the Nats also gave him four runs. This time, Clippard got the win in relief.

Then came the meltdown against Chicago. Zimmerman took responsibility — “I feel bad,” he said — but Ramos said he told Strasburg to never put his head down because when he does, he loses focus. Look at his body language lately. And Manager Davey Johnson pointed out, rightly, that bad things happen behind pitchers all the time.

“He’s too good a pitcher to let adversity behind him let him down,” Johnson said. “He’s certainly capable of picking us up. It’s a team effort. And errors are part of the game.”

They are certainly part of the Nats’ game this season. No other starter has had to deal with seven errors, but Strasburg is not supposed to be like any other starter. He was supposed to have the tools, the mental fortitude and the physical strength to get this team out of jams and to set the tone for the pitching staff — in other words, to be the ace. We’re not seeing that this season. He seems dejected and upset, and while that may be understandable, a good pitcher keeps that off the mound.

And when your ace lets an error get into his head and implodes on the mound, he should take some responsibility. Instead, after the Cubs loss, Strasburg said, “I feel like I’m going out there and pitching well. Just not happening on the days I pitch right now. It’s all going to change. It’s still early, and all I can do is just go out there and give everything I have every fifth day. Whatever happens happens.”

Not exactly the St. Crispin’s Day speech, and certainly not a sign that Strasburg feels he’s in any way responsible for his 1-5 record. But it’s a team game, and the sooner Strasburg remembers that, the sooner he will get back on track.

For previous columns by Tracee Hamilton, visit washingtonpost.