LOS ANGELES — The questions have been asked ad infinitum.

How could the Giants be the best team in the majors in the first half, then the worst in the second half? How can a 57-33 juggernaut take four days off, then go 11-23?

The Giants’ second half seems inconceivable. As they start the first of their three remaining series against the Dodgers on Tuesday night, nobody can look at their entire season and say whether they are good, bad or mediocre.

The final 38 games should provide clarity. Or, heck, maybe not.

“This is where we’re going to see what kind of team we have,” said Johnny Cueto, an honest assessment that even some players are not terribly sure yet.

The offseason will provide plenty of opportunity to dissect this team of polar halves, but if we understand the Giants’ second-half collapse, we might be able to forecast whether the issues can be — or have been — solved ahead of the final six nail-biting weeks of the regular season.

Here is a roughly chronological look at what happened:

Romo’s injury

Three games into his season, Sergio Romo went on the disabled list with an elbow sprain.

The Giants already were adjusting to Jeremy Affeldt’s retirement and entered the 2016 season relying on many unknowns, particularly relatively untested relievers such as Hunter Strickland, Josh Osich and Cory Gearrin.

Romo’s injury so soon into the season forced the staff to jettison their preconceived ideas of roles. With Javier Lopez struggling and the younger relievers inconsistent, it became a matchup bullpen, which meant a lot of appearances for everybody.

That seemed to catch up to them. They lost Gearrin to a shoulder injury in early July, and others continued to carry a heavy workload that probably affected their performance.

Aside from one solid stretch on the last trip, the bullpen remains a question mark and contributed to more losses in the second half than this club is accustomed to. It started with Santiago Casilla’s walkoff balk in the second game after the break and went from there.

The forecast: Issues remain, particularly in middle and long relief. Manager Bruce Bochy might have to play matchups the rest of the way.

Pence, Panik, Duffy injuries

Some teams can withstand the loss of three everyday starters. The Giants actually did, to a point.

They ended the first half 24 games over .500 even with Hunter Pence missing more than a month with a hamstring injury, Joe Panik out 21 games with a concussion and soon-to-be-traded Matt Duffy out 20 games with a hamstring injury.

Conor Gillaspie and Mac Williamson, plus journeymen Ramiro Peña and Grant Green, stepped in successfully and helped the Giants finish the first half with 424 runs, fourth-most in the league.

Ultimately, the Giants missed their regulars, particularly Pence. (Panik and Duffy were not having solid offensive seasons to begin with, but were starting to hit when they got hurt.)

When Panik and Pence returned, they struggled badly and did not provide an expected lift, leading to a stretch in July and August in which they scored two or fewer runs in 12 of 22 games. Not surprisingly, they went 8-14.

The forecast: Pence and Panik have improved. They joined several hot hitters to score 47 runs over the past nine games. That tide seems to have turned.

Cueto’s All-Star Game

Madison Bumgarner and Johnny Cueto were the majors’ best 1-2 combo in the first half. The Giants were 29-8 in their starts, and for two months Jeff Samardzija was nearly as hot. The rotation is always the foundation of the Giants’ success, and their first-half pitching was a big part of that 57-33 record.

Six days after finishing a 13-1 first half, Cueto threw 32 pitches in his All-Star start and lost. Five nights later, he started the second half by losing in San Diego to launch an 0-2, 4.84-ERA stretch of six starts.

All-Star related? Only Cueto can say, and he hasn’t blamed it. He had plenty of rest before and after that game.

Cueto’s short slide, Samardzija’s inability to right himself and ongoing struggles in the fourth and fifth spots have led to a 4.80 ERA by the rotation in the second half, 10th in the league. The starters are 7-17. Combine that with the aforementioned hitting slump, and the second-half slide seems more fathomable.

The forecast: Cueto is coming off a win that resembled his first-half work, and Bumgarner has been Cy Young-worthy. One can imagine them regaining that 1-2 dominance. Everyone saw what Samardzija did Sunday night — his past three starts, really. So it’s not out of line to have higher expectations for the starters over the final 38 games.

The trades

The Giants acquired three players at the deadline, infielder Eduardo Nuñez, starter Matt Moore and reliever Will Smith, to help them now and in future years.

None has had an immediate impact. Nuñez hit .194 in his first 11 games, Moore had two somewhat successful starts followed by two bad ones, and Smith’s ERA as a Giant remains in double digits.

The forecast: Nuñez has turned his hitting around and begun to have a huge impact, but neither of the pitchers has shown signs that he will be a net improvement down the stretch. Their San Francisco sample size is too small to draw any real conclusions.

The schedule

The Giants ended the first half with 26 games against sub-.500 teams and went 19-7. They started the second half by getting swept at San Diego then having to travel to face Boston, the New York Yankees, Philadelphia, Washington and Miami, with Washington, Baltimore, Pittsburgh and the New York Mets at home.

That tougher schedule alone could not explain the Giants’ awful second-half start, but given all their other issues it proved to be an obstacle.

The forecast: Things get easier. The Giants’ only remaining games against currently winning teams are the nine against the Dodgers, four at home against the Cardinals and four at the Cubs. Beyond that they see a whole lot of the bottom of the NL West.

The Giants are 31-18 in the division, including 6-4 against Los Angeles.

Henry Schulman is a San Francisco Chronicle staff writer. Email: hschulman@sfchronicle.com Twitter: @hankschulman

Separate ways

The All-Star Game has become a dividing line for the Giants season:

Hitting

Category Before After Average .263 .256 On-base .336 .330 Slugging .406 .388

Pitching