[11:26:13] [Server thread/ERROR]: Could not pass event EntityDamageByEntityEvent to CombatLog v1.8.11 org.bukkit.event.EventException at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:302) ~[spigot.jar:git-PaperSpigot-"8b18730"] at co.aikar.timings.TimedEventExecutor.execute(TimedEventExecutor.java:78) ~[spigot.jar:git-PaperSpigot-"8b18730"] at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[spigot.jar:git-PaperSpigot-"8b18730"] at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:501) [spigot.jar:git-PaperSpigot-"8b18730"] at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:486) [spigot.jar:git-PaperSpigot-"8b18730"] at org.bukkit.craftbukkit.v1_8_R3.event.CraftEventFactory.callEvent(CraftEventFactory.java:87) [spigot.jar:git-PaperSpigot-"8b18730"] at org.bukkit.craftbukkit.v1_8_R3.event.CraftEventFactory.callEntityDamageEvent(CraftEventFactory.java:553) [spigot.jar:git-PaperSpigot-"8b18730"] at org.bukkit.craftbukkit.v1_8_R3.event.CraftEventFactory.handleEntityDamageEvent(CraftEventFactory.java:466) [spigot.jar:git-PaperSpigot-"8b18730"] at org.bukkit.craftbukkit.v1_8_R3.event.CraftEventFactory.handleLivingEntityDamageEvent(CraftEventFactory.java:585) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.EntityLiving.d(EntityLiving.java:1112) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.EntityHuman.d(EntityHuman.java:860) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.EntityLiving.damageEntity(EntityLiving.java:748) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.EntityHuman.damageEntity(EntityHuman.java:801) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.EntityPlayer.damageEntity(EntityPlayer.java:504) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.EntityHuman.attack(EntityHuman.java:1002) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.EntityPlayer.attack(EntityPlayer.java:1086) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.PlayerConnection.a(PlayerConnection.java:1382) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.PacketPlayInUseEntity.a(SourceFile:52) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.PacketPlayInUseEntity.a(SourceFile:11) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.PlayerConnectionUtils$1.run(SourceFile:13) [spigot.jar:git-PaperSpigot-"8b18730"] at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_121] at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_121] at net.minecraft.server.v1_8_R3.SystemUtils.a(SourceFile:44) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:774) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:378) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:713) [spigot.jar:git-PaperSpigot-"8b18730"] at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:616) [spigot.jar:git-PaperSpigot-"8b18730"] at java.lang.Thread.run(Thread.java:745) [?:1.8.0_121] Caused by: java.lang.NoClassDefFoundError: com/massivecraft/factions/entity/BoardColls at com.jackproehl.plugins.listeners.EntityDamageByEntityListener.tagAttacker(EntityDamageByEntityListener.java:115) ~[?:?] at com.jackproehl.plugins.listeners.EntityDamageByEntityListener.onEntityDamageByEntity(EntityDamageByEntityListener.java:50) ~[?:?] at sun.reflect.GeneratedMethodAccessor393.invoke(Unknown Source) ~[?:?] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121] at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121] at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:300) ~[spigot.jar:git-PaperSpigot-"8b18730"] ... 27 more
This is an issue with the CombatLog plugin on your server, you're also using PaperSpigot, this is the Spigot forums.
Change your server to Spigot (Insert Version Here) and then redownload the (Version of server) CombatLog