A needle assembly with a needle shield is disclosed. The shield includes alumen slidable on the needle, a holder and a needle blocking object whichmoves at least partially into the lumen in order to block distal movement ofthe needle. A spring biases the blocking object towards the needle axis.Proximal movement of the needle relative to the shield is limited by arestraint in the form of a discontinuity on the needle which abuts the shield,a tether or a tube abutting the needle hub. When the needle shield moves froma non-shielding position to a shielding position, the needle blocking objectmoves at least partially into the lumen. The needle blocking object isradially and axially constrained in the shielding position. The holder alsoprevents radial, longitudinal and circumferential movement of the blockingobject. In one embodiment, the needle blocking object is a ball. A catheteradapter and tube may be threaded over the needle. The needle blocking objectmay also lock the catheter adapter to the needle shield, allowing it to bereleased only when the needle is shielded.
