Mantha, who was Winnipeg's second choice (23rd overall) of the 1980 Entry Draft, didn't really feel comfortable in the NHL until the 1983-84 season when he exploded for 16 goals, 38 assists and 54 points. Despite the great improvement, Mantha was shipped to Pittsburgh at season's end to complete a deal for Randy Carlyle, who was one of the top defensemen in the league at that time.
Mantha enjoyed 3 really good seasons in Pittsburgh. His first year saw him score 11 times and 40 helpers. In 1985-86 he enjoyed his best statistical year, scoring 15 goals and 67 points. A fractured wrist and a thigh injury shortened his 1986-87 season to just 62 games, in which he scored 9 goals and 40 points.
Despite Mantha's contributions, he wasn't the typical offensive defenseman that teams coveted. Paul Coffey was the prototypical scoring rearguard at the time - able to rush the puck from end to end with blazing speed and perfect passes. Mantha was an above average skater and a good puckhandler but was more of a breakout player. He'd pass the puck out of his zone rather than lug it up ice. Mantha was a decent pointman on the powerplay, but was never a true "quarterback." He read plays very well and liked to jump into the slot for scoring chances. On weaker teams he'd be a good PP player, but ideally he was best suited as the second man on the point. Defensively Mantha was only average. Despite his size, he was not a physical player and he lacked intensity on a consistent basis.
When Paul Coffey became entangled in a contract dispute with the Oilers, the Pens became the most interested team in his services. Part way through the 1987-88 season they got their man but at a steep price - Craig Simpson, Dave Hannan, Chris Joseph and Mantha in exchange for Coffey, Dave Hunter and Wayne Van Dorp.
However Mantha never fit in in Edmonton. Perhaps it was the pressure of having to "replace" Coffey, or maybe he just wasn't suited for the Oilers style of play. Mantha was very ineffective in just 25 games with Gretzky and Co., collecting just 6 assists. The Oilers moved him to Minnesota in exchange for veteran speedster Keith Acton before the end of the year.
Mantha was never quite the same from that point on. Maybe it was partly due to having to live with the stigma of being traded for Paul Coffey, although he battled some injuries along the way too. He bounced from Philadelphia to Winnipeg to the 1992 US Olympic Team and briefly back to Philly before ending his playing career in 1993.
Mantha has since turned to coaching in his post playing days.