/scoreboard players set ''Red_Team_Kills'' displayBoard 0
/scoreboard players set ''Blue_Team_Kill''s displayBoard 0
/execute as @a[team=''redTeam'',scores={''killedSomeone''=1..}] run scoreboard players operation ''Red_Team_Kills'' ''board'' += @s ''killedSomeone''
/execute as @a[team=''blueTeam'',scores={''killedSomeone''=1..}] run scoreboard players operation ''Blue_Team_Kills'' ''board'' += @s ''killedSomeone''