Roger had a monsterous minor league career. Check out those numbers as he came up the ranks in 1968 (31, 103 .289), 1969 (22, 90 .298 in the Texas League, which has always been a pitcher's league) and 1970 as the International League MVP (24, 130 .334). Nobody likes to do this, but he came back to AAA ball with the 1976 Denver Bears, hitting 42 homers and winning the league MVP. It's a good sign for a major leaguer to be the MVP 6 years apart, but nobody wants to win a second MVP at a minor league level.
I think Baltimore must have recognized Roger's talent being a little one-dimensional as he was coming up. They didn't have room in the outfield for him and sent him to the Phillies for Grant Jackson. Jackson had a good career with the O's, but Roger couldn't get established for the Phils.
The Phils gave him a shot in 1971 with a lot of playing time in right field, but he didn't hit like they'd wanted. I don't think the Phillies would have been disappointed with him finishing 4th on the team in homers as a rookie, but for that number to be only 6 homers (tied with Oscar Gamble, Joe Lis and Rick Wise) was a disappointment. He also didn't hit for average and struck out a lot. His playing time reduced in 1972, sharing time with Tommy Hutton, Mike Anderson and Gamble. He still didn't hit for average, had disappointing power and struck out too much.
He wandered around after that, through the minors with the Indians, Reds and Expos. He even had a year in the Mexican League. After his monster year with Denver in 1976, the woeful Cardinals took a flyer on him in the Rule 5 draft (largely because Vern Rapp had managed him in the minors) and he had a great year as a pinch-hitter (5 homers, 11 walks and only 9 strikeouts in 83 at bats). Did I mention he also hit .398! His production as a pinch-hitter declined and after a couple of more years the Cards released him.
Before being released, he had one of those magic moments. Bottom of the 11th, bases loaded, 2 out. Astros scored three in the top of the 11th, so this is it. Astros have Joe Sambito on the hill, and he's one of the top relievers in the league. The air in the stadium was deflated because Garry Templeton had just struck out for the 2nd out. Freed pinch hits for Jerry Mumphrey as the last chance. Bang! Game-winning grand slam! A loser becomes a winner. Way to go, Roger!
Roger had heart trouble and died at age 49 in 1996. When googling him, I found a link to help find his gravesite, for anyone who's into that.