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:"mainhand",type:"knockback_resistance",id:"5555",amount:.2,operation:add_value}
execute if score random itemcount matches 2 run data modify entity @s Item.components."minecraft:attribute_modifiers" append value {slot:"mainhand",type:"knockback_resistance",id:"5555",amount:.1,operation:add_value}
execute if score random itemcount matches 3 run data modify entity @s Item.components."minecraft:attribute_modifiers" append value {slot:"mainhand",type:"knockback_resistance",id:"5555",amount:-0.1,operation:add_value}
execute if score random itemcount matches 4 run data modify entity @s Item.components."minecraft:attribute_modifiers" append value {slot:"mainhand",type:"knockback_resistance",id:"5555",amount:-0.2,operation:add_value}
scoreboard players reset random