Hey James Mirtle, you're not the first one, but you're confusing the words 'core' and 'corps' when you write:
"Goaltenders James Reimer and Jonas Gustavsson have become the most popular targets after a few tough outings, although head coach Ron Wilson and the team’s defence core are also drawing fire."
core (kôr, kr)
1. The hard or fibrous central part of certain fruits, such as the apple or pear, containing the seeds.
2. The central or innermost part: the hard elastic core of a baseball; a rod with a hollow core.
3. The basic or most important part; the essence: a small core of dedicated supporters; the core of the problem.
n pl corps [kɔːz]
1. (Military) a military formation that comprises two or more divisions and additional support arms
2. (Military) a military body with a specific function intelligence corps medical corps
3. a body of people associated together the diplomatic corps
You may discuss a team's core, or the core forwards, for example, when referring to those most central to its success or future, its more trusted veterans or promising rookies. If you speak of the Canadiens' defensive core, you would be referring to Josh Gorges and P.K. Subban, maybe Alexei Emelin, and certainly Andrei Markov, whenever he returns from injury. The others (Yannick Weber, Raphaël Diaz, Tomas Kaberle, Chris Campoli) would be considered peripherals, not part of the core.
What you meant though is the Leafs defencemen as a whole, its defensive 'corps'.
Don't worry, you're not the first one to make this mistake, and your editors dropped the ball, they should have caught it too. Just get it right in the future.