Adapter protein that plays a role in T-cell receptor (TCR)-mediated activation of signaling pathways. Required for T-cell activation and integrin-mediated T-cell adhesion in response to TCR stimulation. Interacts with SKAP1, LCK and FYN. The phosphorylated form interacts with LCP2. Recruited to membrane rafts and immunological synapse after TCR stimulation. Phosphorylation is required for its function in T-cell activation.