Of all the utterly bewildering developments during the Giants 0-5 start to the season, none has been quite so confounding as Eli Manning and his unfortunate knack for tossing interceptions.

Manning threw three more picks in the Giants' 36-21 loss to the Eagles on Sunday, boosting his tally to a league-leading 12 this season and inviting serious questions about whether the Giants' franchise player is actually hurting the team's chances of winning.

Giants quarterback Eli Manning (center) is off to a dismal start. Reuters

In a conference call Monday, head coach Tom Coughlin absolved his quarterback from blame for the cluster of picked-off passes, pointing the finger instead at a struggling offensive line, poor route-running by wide receivers and a couple of instances of bad luck.

But the biggest reason behind Manning's sudden spike in interceptions is that he seems to have developed a troublesome addiction to the deep ball.

No quarterback in the NFL has heaved the ball downfield this season more often than Manning. He has attempted 33 passes that have travelled at least 20 yards through the air, according to Stats LLC. That's more than six deep shots per game.

Excluding a dozen passes that were either thrown away or batted down, roughly 17% of Manning's 191 total attempts have been long passes. Should he continue to fling the ball downfield at his current pace, Manning will finish the season with the second-highest percentage of deep passes by any quarterback in the past three years, behind Tim Tebow's 2011 season in Denver.

"They throw the ball deep a lot," said Eagles cornerback Brandon Boykin, who snagged one of Philadelphia's three interceptions Sunday. "Most of the time it's run, run, deep ball. Or just off the bat he looks to go deep and make a play."

It's not exactly news that the Giants like to take their shots downfield. Manning has earned two Super Bowl MVP awards thanks in large part to his willingness to launch long passes toward wide receivers like David Tyree and Mario Manningham.

Now that those passes are routinely landing in the hands of defenders, Manning's predilection is becoming a problem.

For starters, four of his 12 interceptions have come on those deep shots, while only two of the long passes have resulted in touchdowns. But more than that, the time it takes Manning to go deep is giving pass rushers the opportunity to put more pressure on him, resulting in the sorts of ill-advised passes that became three fourth-quarter turnovers on Sunday.

In order to allow receivers to get open downfield, Manning has been holding the ball for an average of 2.75 seconds per pass attempt, according to the statistical outlet Pro Football Focus, his longest stretch of time since they began tracking this metric in 2011. Consequently, he's been under pressure on 40.7% of his dropbacks, up from 29.8% last season, and is frequently forced to throw under duress, leaving him susceptible to interceptions by robbers and underneath defenders.

Granted, Manning can't simply abandon the bomb. The Giants' running game has been woeful this season, producing two touchdowns and an average of just 3.3 yards per carry. The short-passing game may be even worse, leaving them with no bread-and-butter plays with which to move the chains.

Given how badly the Giants have struggled to move the ball, former NFL safety John Lynch says it's understandable that Manning has become hung up on going deep, even if it results in a glut of ugly interceptions.

"Sometimes your greatest strengths are your greatest weaknesses," said Lynch, now a football analyst for Fox Sports. "He's trying to make a play by throwing downfield. Those passes that can often lead to turnovers, but Eli doesn't worry about protecting his stats. He just wants to put his team in a position to win."

Write to Jonathan Clegg at jonathan.clegg@wsj.com