The oldest of three hockey playing brothers (with
Bill and
Bob), Plager played junior league hockey with the
Peterborough Petes of the
Ontario Hockey Association before spending six seasons in the minor leagues, cementing a reputation as a hard-nosed defensive defenceman. His reputation was established while still in juniors, when he had a notable fight with his own brother
Bob, who was playing for the rival
Guelph Royals. Plager spent the
1964 season with the
Omaha Knights of the
Central Professional Hockey League (CPHL), leading the league in assists and winning best defenceman accolades before being sold by the
Detroit Red Wings to the
Montreal Canadiens for $20,000. He played the majority of the next three seasons with the
Springfield Indians of the
AHL. With the
1967 NHL Expansion, many new jobs opened up in the
National Hockey League, and Plager was acquired with
Red Berenson by the St. Louis Blues from the
New York Rangers, which held his rights. The deal proved extremely successful for the Blues, for Berenson became the first great offensive star of the newly minted Western Division, while Plager anchored a stingy defence that allowed the fewest goals in the NHL in
1969, the second fewest in
1970, and the third fewest in
1971. Behind Plager's leadership—he was named the second captain in team history in 1970, the Blues made the
Stanley Cup finals their first three seasons. The three Plager brothers played together for four seasons in St. Louis, with Barclay and Bob together on the Blues' defence for eleven seasons, then widely seen as the "Plagers' team". ==Post-NHL career==