Pa Modou Kah, right, has been part of Portland's woeful back line, which has conceded the most goals in the last 15 minutes of games in MLS. (David Blair/Icon SMI)

PORTLAND, Ore. — The Portland Timbers painted the walls of the locker room at their training ground in preseason to reflect the team's philosophy under second-year head coach Caleb Porter.

One wall spells out the team's attack: "The one who has the ball is the master of the game." Another deals with the opposite side of the game: "Defending is like breathing; you must do it to survive."

Right now, the Timbers, who were a game away from reaching the 2013 MLS Cup, are on life support, at the bottom of Major League Soccer's Western Conference with six ties and nine total points from 10 league matches. For how detail-oriented Porter appears in preparing his team for games, it's the same small aspect that keeps burning them.

On Sunday against the LA Galaxy, Mamadou Danso was the guilty party, allowing a long throw-in from Dan Gargan to bounce between him and goalkeeper Donovan Ricketts. The only other player within five yards of the ball, Robbie Keane, darted in to score his fifth goal of the season in the 92nd minute.

"I'm sounding like a broken record after games, because most of the goals we're giving up are simple crosses and guys running through to head the ball in. At this level, it's unacceptable to give up those type of goals," Porter said after the Timbers' 1-1 draw with the Galaxy. "It's a simple thing to do: you pick up your guy, and you head the ball out. We're not picking guys up; we're letting guys float free. We're not making plays there, and it's costing us."

It's not just Danso who has been caught ball-watching on the Timbers' back line this season.

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New acquisition Norberto Paparatto has already been benched for his defensive shortcomings as a center back. Alvas Powell failed to track Clint Dempsey in the penalty area when he scored the Sounders' third goal in a wild 4-4 tie in which Portland led by two goals at one point. Pa Modou Kah didn't follow Erick Torres when he scored in the 79th minute on April 12 to save a point for Chivas USA.

"If you look back on the times we've been burned and the goals that we've given up to drop points, it's been the same trend," Porter said. "You talk about it, you show video on it, you train it, you give them the keys to the game, the important things, and for me, at this level, I don't know how it happens. Late in the game, Robbie Keane — how is he naked to head the ball in the goal?"

It's also the timing of these goals that kills the Timbers' momentum, and in only one of those games — a 3-2 home win over D.C. United on May 3 — have they taken all three points. Portland has conceded seven goals in the last 15 minutes of games this season, the worst mark in MLS.

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But the trend of failing to defend simple crosses didn't start in 2014; in Porter's first season as coach in 2013, in which he was the MLS Coach of the Year, his team's biggest shortcoming was what he likes to call "box defending": situations inside its own penalty area.

"If we want to go anywhere as a team, you've got to defend crosses," he said. "It's simple, because a lot of goals in this league are scored on crosses — set pieces and crosses."

The team's defenders had several shaky moments outside the Portland penalty area in possession against L.A. as well. Anytime the Galaxy pressured high as a unit, the defenders would either play an unfavorable ball toward a teammate or panic and hit it long.

Even with an attack that features weapons as dangerous as Darlington Nagbe, Diego Valeri and Gastón Fernández, Portland will be fighting an uphill battle until the back four is sorted out. Particularly at center back, none of the players who have seen the field have shown competency in Porter's desired possession style or the kind of scrappy defending inside their own penalty area that MLS dictates as necessary.

Until that solid base is established, building out of the back will be extremely difficult, and the team will continue to leak goals in straightforward situations. The solution is to either buy more players — general manager Gavin Wilkinson just returned from a scouting mission to Europe — or to shuffle personnel.

"We're running out of time. We need to pick it up, and we need to change that trend," Porter said. "It's time to change it. Otherwise, we're not going to be the team we want to be at the end of the year."

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Two rookie center backs who haven’t played any MLS minutes yet are Taylor Peay and Bryan Gallego. Peay captained University of Washington last year, leading with his hard-nosed play in the back, while the smaller Gallego started for Porter’s old college team at Akron before signing a Homegrown Player contract with the New York Red Bulls and ultimately being traded to Portland.

The two young players — Peay is 22; Gallego is 21 — lack professional experience, but they would seem to complement one another’s skills in a classic ball winner-distributor partnership. One potential drawback is that Gallego might not be big enough for the physicality of MLS, which might not help him win balls in the air any better than Danso or Kah.