מלכים ב, פרק י״א, פסוק ט׳

Jehoiada the priest's carefully calculated plan is set into motion as the military commanders mobilize their troops directly from the Temple guards. Each captain gathers his specific unit of soldiers to form the necessary security detail [רד״ק, מצודת דוד].

To build this force, the commanders combine the guards who are transitioning during the Sabbath. They take only half of the incoming shift, but merge them with the entire outgoing shift. This strategy stems from a highly practical consideration by Jehoiada. By utilizing the troops who are already present at the Temple during the shift change, he avoids the need to summon outside guards or trouble additional units to arrive specifically for this mission [רלב״ג].