Acts as a component of the essential kinetochore-associated NDC80 complex, which is required for chromosome segregation and spindle checkpoint activity (PubMed:12351790, PubMed:14654001, PubMed:14699129, PubMed:15062103, PubMed:15235793, PubMed:15239953, PubMed:15548592, PubMed:16732327, PubMed:30409912, PubMed:9315664). Required for kinetochore integrity and the organization of stable microtubule binding sites in the outer plate of the kinetochore (PubMed:15548592, PubMed:30409912). The NDC80 complex synergistically enhances the affinity of the SKA1 complex for microtubules and may allow the NDC80 complex to track depolymerizing microtubules (PubMed:23085020). Plays a role in chromosome congression and is essential for the end-on attachment of the kinetochores to spindle microtubules (PubMed:23891108, PubMed:25743205). {ECO:0000269|PubMed:12351790, ECO:0000269|PubMed:14654001, ECO:0000269|PubMed:14699129, ECO:0000269|PubMed:15062103, ECO:0000269|PubMed:15235793, ECO:0000269|PubMed:15239953, ECO:0000269|PubMed:15548592, ECO:0000269|PubMed:16732327, ECO:0000269|PubMed:23085020, ECO:0000269|PubMed:23891108, ECO:0000269|PubMed:25743205, ECO:0000269|PubMed:30409912, ECO:0000269|PubMed:9315664}. This is the function of NDC80 (NDC80 kinetochore complex component, Ensembl gene identifier ENSG00000080986).