Acts as a component of the essential kinetochore- associated Ndc80 complex; which is required for chromosome segregation and spindle checkpoint activity during meiosis and mitosis. Required for kinetochore integrity and the organization of stable microtubule binding sites in the outer plate of the kinetochore. Participates in SAC signaling that responds specifically to disruptions in spindle microtubule dynamics (By similarity). {ECO:0000250|UniProtKB:Q9V3V7}.