CPV code 45212221 designates Construction work in connection with structures for sports ground in the Common Procurement Vocabulary (CPV 2008), the EU classification used to describe the subject of public contracts.
45212221 is a leaf code — the most specific level of its branch — so it can be used directly as the main CPV code of a contract notice. If it does not quite fit, check the neighbouring codes under 45212220 (Multi-purpose sports facilities construction work).