The Giants were left at the altar by a couple of high profile free agents this offseason and did their best to improve the roster in different ways. Listen to Brian Sabean talk before the FanFest this weekend, and what they ended up doing was look at ways to “deepen the roster.”

One of those ways was to invite their many starting pitchers back into the fold. Behind new horse Madison Bumgarner and returning horse Matt Cain, the Giants will slide in some combination of Tim Hudson, Jake Peavy, Ryan Vogelsong, Tim Lincecum, and Yusmeiro Petit.

That collection of names may not lead the Giants into the next decade, but the veterans are mostly capable of league-average (or so) work. That’s impressive depth, actually. Given that there’s a 65% likelihood that two starters are on the disabled list at the same time on the average team — and this team may be more likely than most to have starters get injured, given their collective age — it’s good that the Giants score well on our depth charts in different ‘depth’ metrics.

Below, see how the Giants rank when it comes to innings expected from their sixth and seventh starters, projected Wins Above Replacement from those slots, and WAR per 200 innings pitched from their sixth and seventh starters. Generally, the Giants look like a top-five team when it comes to starting rotation depth.

You can’t always go home with the belle of the ball. As Dave Cameron has pointed out before (with respect to the Athletics), it’s savvy to work around the edges and improve wherever you can, even at the sixth and seventh starter spots.

That doesn’t mean that the team is collectively ready to take the next step forward and defy convention. We know that pitchers do poorly the third time through the order, and that the Giants could benefit from ‘piggybacking’ starters, should the current roster allow for it.

Piggybacking — pairing starters for three-to-four inning stretches in the same game — happens right now. In the low minors, it helps young pitchers that need to stretch out. It’s used for the same reasons in Spring Training.

In the playoffs, we did see it in action for the Giants, as manager Bruce Bochy saved Yusmeiro Petit as safety blankets for certain starters in certain situations. Before FanFest, Bochy even referenced the possibility of using his starting rotation depth that way, but his pitching coach isn’t a huge fan.

For one, there are financial implications for the players that could make for an uncomfortable clubhouse. “You tell that starter you’re going to take him out before he gets his win and you’ll have the clubhouse turned upside down,” said pitching coach Dave Righetti.

Righetti admitted that the current roster allows for that sort of thinking –“It’s a great question and you do have to keep your thoughts open to different things” — but just didn’t think it would fly. “Till you see a guy fall down and need help, you don’t baby people here in the big leagues,” he said.

But there was something more important. A reason not to piggyback for a season. “The reason: you lose,” Righetti said. “Colorado tried it. It’s not healthy. I’m positive.”

It seems a bit unfair to call a practice that’s regularly-used in the minors and in the spring unhealthy. Maybe Righetti is referring mostly to the situation in Colorado, which admittedly didn’t turn out so great. It’s true that Drew Pomeranz and Christian Friedrich, the two younger starters in that 2012 piggyback rotation, missed large portions of 2013 due to injury. It’s also true that many pitchers get injured, and that the veterans — Jeff Francis and Jeremy Guthrie — didn’t see those same effects.

As for how well it worked out, we also probably shouldn’t point to one half-season effort and call the whole thing a failure. Just like with the injury side.

That isn’t to say that Righetti is wrong, of course. Spring Training and the minors are different, and in particular, they are different because of roster restrictions. Most staffs have 12 pitchers. If four pitchers on that active roster do the work of two starters, the other five will somehow have to absorb the 100+ innings that those two relievers would normally pitch. That could cause unhealthy usage from the other relievers. That could cause injury, even if not necessarily to the four starters that are now pitching on regular rest (but not pitching to as many batters).

Is there a golden ratio, where you avoid seeing that iffy starter a third time through the order, and yet you get enough innings out of your four piggybacked starters to replace the missing two relievers?

The league’s starters saw 4.2 batters per inning as a group. That means your league average pitcher could see 18 batters in 4.3 innings. Let’s give him four innings. Let’s give your second league average starter four more innings. You’ve now gotten eight innings from your two starters. Your league average starter averaged six innings per start. So you save two innings per piggyback start, and over the course of the season, you would theoretically save 120 innings total.

Now your pen has to absorb 10-20 more innings at most — and if you had a particularly versatile bench, you might be able to do that by running a 13-man staff out there. The benefits of having your two worst starters never see a lineup a third time through are established — batters are 13% better, relative to themselves, when they see a pitcher the third time in a game.

You might have noticed the catch. Your four starters should probably be around league average to make this work, at least in terms of work load (and even then there are 30 innings to account for). In the case of the Giants, they might seem like they aren’t far off from having four league-average starters. Pro-rate their projections to 200 innings, though, and their four worst pitchers among the seven possible starters are Jake Peavy (1.2 WAR/200), Ryan Vogelsong (.6 WAR/200), Tim Lincecum (1.4 WAR/200), and Yusmeiro Petit (3.6 WAR/200 because FIP loves him, and because he’s partially projected as a reliever). Since two wins above replacement is the shorthand for league average, this staff actually seems a bit short. Then again, all four of these pitchers would pitch better if they didn’t have to go long into games.

If players weren’t still paid at least partially based on how many wins they got. If your four starters could pitch up to league-average status by avoiding the third time through the lineup. If the rest of your relief staff could absorb 30 or so extra innings without health implications. If your versatile bench would allow for an extra reliever. If your particular players would accept the innovation as something that would help them and the team at the same time.

If most of these things were true, it might make sense to set up a rallying cry for the Giants to piggyback their final two rotation spots this year. As a team, they might be best suited for the second attempt at the strategy — three of the four pitchers are veterans that may not see another great contract, and the fourth is the most likely to be a swing man if the team doesn’t adopt the strategy, so there’s not much to lose. With the World Series hardware in hand, they could ask their pitchers to try something new. Their collection of arms could play up to the level that is needed for something like this to work, too.

They’d just need to get their pitching coach to like the idea.