Walker’s best season came in 1970, when he went 15-6, mostly as a starter (3-1, three saves in relief); his 3.04 ERA, .714 winning percentage, and 7.1 hits per nine innings all ranked third in the NL. He took a tough loss in Game Two of the LCS, giving up just one earned run to the Reds in seven innings. He fell off in 1971, going 10-8 with a 3.54 ERA for the World Champion Pirates but almost had a no-hitter against the Dodgers; he gave up a ninth-inning HR to Joe Ferguson. In the World Series, he had a disastrous start in Game Four (the first night game in Series history), retiring only two batters and giving up three runs, but the Pirates won 4-3. In 1972 Walker was bothered by a stiff back and finished 4-6 with a 3.40 ERA in limited use. He declined further in 1973 (7-12) and was sold to the Tigers for his last season.
Walker was a notoriously bad batter who went without a hit in 1969 (32 at-bats) and was 0-for-39 in 1972 before finally getting a hit, and a rousing ovation, in July. His lifetime average of .059 is the eighth worst of all time for a pitcher (100-plus at-bats).