中堅

What does 中堅 mean in English?

1. nucleus; backbone; mainstay; key figure(n)
2. medium-level; mid-level; middle-ranking; midsize(adj-no, n)
3. main body (of troops); crack troops; select troops(n)
4. center field; centre field; center fielder; centre fielder(n)
5. athlete competing in the middle-number match in a team competition, i.e. second in 3-on-3, third in 5-on-5 (kendo, judo, etc.)(n)