Definition
Force Middle (FM) is a defensive call in which the front layer — typically two defenders — forces the disc toward the central channel of the field rather than toward a chosen sideline. Each front defender takes one side of the thrower; the throw the offence is given is into the middle, where the defence is set up to attack it.
In Context
FM is the headline call of our 2-4-1 FM Zone. It looks paradoxical — we coach the offence to attack the middle, and now we are giving the middle away on defence — but the trick is that we are not really giving it away. The middle is where the next two defenders (the mids) are stacked, ready to attack any throw that comes through.
FM is a coordinated defence. The two front defenders must be willing to switch sides as handlers move — see 2-4-1 FM Zone for the full mechanics. A silent FM where the front pair don't communicate the switch is worse than a normal force, because both front defenders end up on the same side and the throw goes around them uncontested.
FM is also wind-friendly. The middle throws it forces are typically short, into traffic, and easy to disrupt with mids and a high-positioned deep. A long swing or huck out of FM is exactly the throw the wind makes hardest.