A materials reduction apparatus comprising: a rotatably mounted rotor having radial projections; an anvil having an operational configuration where the anvil is operational fixed in proximal relation to the projections of the rotor; a conveying mechanism for conveying materials to be reduced into the rotating rotor and projections, and to be carried by said projections for impacting said anvil to reduce in size the components of said materials; a screen also having an operational configuration where the screen is operational fixed in proximal relation to said projections of the rotor for engaging said components to further reduce the size of the components and to provide passage of said further reduced components through screen openings in said screen and out of the path of the projections for collection and conveyance away from said apparatus; said anvil and screen mounted to have common pivotal movement away from said rotor projections and as pivoted away from said projections providing a bypass for materials carried by said projections to thereby avoid anvil and screen reduction; and a pivotal resist member adapted to provide resistance to said pivotal movement while permitting said pivotal movement and thus providing a bypass of materials in response to a determined force generated by reduction resisting components of the material, and further adapted to allow the screen and anvil to reestablish the operational configuration, characterized in that said pivotal resist member includes a latch mechanism and further including a spring biased cam member engaging a cam surface, and said reduction by said screen and anvil urges said cam member against said spring bias for retraction and release of said cam member in response to excessive reduction resistance and allows for reattaching once the material has bypassed, and wherein said cam surface is provided by a slidable member urged into a first slidable position in a first slidable direction by a biasing member and a stop that prevents further movement in said first slidable direction, said biased cam member not urging said slidable member in said first slidable direction against said stop when said anvil and screen are urged away from said projections and said biased cam member urging said slidable member against said biasing member for closing of said bypass. a rotatably mounted rotor having radial projections; an anvil having an operational configuration where the anvil is operational fixed in proximal relation to the projections of the rotor; a conveying mechanism for conveying materials to be reduced into the rotating rotor and projections, and to be carried by said projections for impacting said anvil to reduce in size the components of said materials; a screen also having an operational configuration where the screen is operational fixed in proximal relation to said projections of the rotor for engaging said components to further reduce the size of the components and to provide passage of said further reduced components through screen openings in said screen and out of the path of the projections for collection and conveyance away from said apparatus; said anvil and screen mounted to have common pivotal movement away from said rotor projections and as pivoted away from said projections providing a bypass for materials carried by said projections to thereby avoid anvil and screen reduction; and a pivotal resist member adapted to provide resistance to said pivotal movement while permitting said pivotal movement and thus providing a bypass of materials in response to a determined force generated by reduction resisting components of the material, and further adapted to allow the screen and anvil to reestablish the operational configuration, characterized in that said pivotal resist member includes a latch mechanism and further including a spring biased cam member engaging a cam surface, and said reduction by said screen and anvil urges said cam member against said spring bias for retraction and release of said cam member in response to excessive reduction resistance and allows for reattaching once the material has bypassed, and wherein said cam surface is provided by a slidable member urged into a first slidable position in a first slidable direction by a biasing member and a stop that prevents further movement in said first slidable direction, said biased cam member not urging said slidable member in said first slidable direction against said stop when said anvil and screen are urged away from said projections and said biased cam member urging said slidable member against said biasing member for closing of said bypass.