A fateful and tense encounter unfolds near the great stone in Gibeon, setting the stage for a carefully calculated assassination. As Joab and his men wait by the stone, Amasa approaches them, returning with his own men, likely en route to the king in Jerusalem [ביאור שטיינזלץ, אברבנאל, רד״ק]. Joab's choice of clothing for this meeting is highly deliberate. While some commentators view the description of his attire as a simple account of his garments [רלב״ג, מצודת ציון], others note that he is specifically wearing a recognized military uniform [רד״ק]. By dressing in the official garb of the army commander, Joab aims to publicly project that his high-ranking status has not been stripped from him [מלבי״ם].
The core of Joab's deception lies in how he carries his weapon. He straps his sword to his waist inside its sheath, making sure it is tightly secured to his body [רד״ק, מצודת ציון]. The primary approach among commentators is that Joab plans in advance for the sword to fall in order to eliminate any suspicion from his target. To achieve this, he avoids the standard practice of hanging the sword on his thigh. Instead, he ties it horizontally across his waist, pressing it closely against himself [רש״י, מצודת דוד, רלב״ג].
As Joab steps forward to greet Amasa, the sword falls to the ground. Because the weapon is positioned horizontally and is smooth, Joab only needs to bend down slightly—perhaps under the guise of adjusting his shoe—allowing the sword to slide out and fall naturally without him actively drawing it [רש״י, מצודת דוד]. Another perspective suggests that the sheath itself is wider than the sword, so when the sheath slips from his waist, the blade falls out on its own [מלבי״ם].
This staged accident is perfectly designed to deceive Amasa. Joab bends down and retrieves the fallen sword with his left hand. By making the weapon's appearance look like an innocent mishap, he ensures that Amasa completely lowers his guard. Joab then steps close, using his free right hand to grasp Amasa's beard in a traditional gesture of greeting, all while the drawn sword waits ready in his left hand [רד״ק, אברבנאל, מצודת דוד].