execute store result score random itemcount run random value 1..4
execute if score random itemcount matches 1 run data modify entity @s Item.components."minecraft:attribute_modifiers" append value {slot:"head",type:"knockback_resistance",id:"1111",amount:.1,operation:add_value}
execute if score random itemcount matches 2 run data modify entity @s Item.components."minecraft:attribute_modifiers" append value {slot:"head",type:"knockback_resistance",id:"1111",amount:.05,operation:add_value}
execute if score random itemcount matches 3 run data modify entity @s Item.components."minecraft:attribute_modifiers" append value {slot:"head",type:"knockback_resistance",id:"1111",amount:-0.05,operation:add_value}
execute if score random itemcount matches 4 run data modify entity @s Item.components."minecraft:attribute_modifiers" append value {slot:"head",type:"knockback_resistance",id:"1111",amount:-0.1,operation:add_value}
scoreboard players reset random