OnEntityDeath

using System.Linq;
using System;
using System.Collections.Generic;
using Newtonsoft.Json;
using Oxide.Core;

namespace Oxide.Plugins
{
    [Info("Kill Reward Items", "RustPluginGenerator", "1.0.0")]
    [Description("Gives players a configurable item stack when they kill another player")]
    public class KillRewardItems : RustPlugin
    {
        private const string PermEnabled = "killrewarditems.enabled";

        private class PluginConfig
        {
            [JsonProperty("Item shortname")]
            public string Shortname = "scrap";

            [JsonProperty("Item amount")]
            public int Amount = 10;

            [JsonProperty("Only for players with permission")]
            public bool PermissionOnly = false;
        }

        private PluginConfig config;
        private bool shortnameWarningSent;

        protected override void LoadDefaultConfig() => config = new PluginConfig();

        protected override void LoadConfig()
        {
            base.LoadConfig();
            try
            {
                config = Config.ReadObject<PluginConfig>();
                if (config == null) throw new Exception();
            }
            catch
            {
                PrintWarning("Configuration file is invalid, using defaults");
                LoadDefaultConfig();
            }
            SaveConfig();
        }

        protected override void SaveConfig() => Config.WriteObject(config);

        protected override void LoadDefaultMessages()
        {
            lang.RegisterMessages(new Dictionary<string, string>
            {
                ["Reward"] = "You received {0}x {1} for killing {2}.",
                ["InvalidItem"] = "The configured reward item shortname is not valid."
            }, this);
        }

        private void Init()
        {
            permission.RegisterPermission(PermEnabled, this);
        }

        private string Msg(string key, string userId = null, params object[] args)
            => string.Format(lang.GetMessage(key, this, userId), args);

        private void OnEntityDeath(BaseCombatEntity entity, HitInfo info)
        {
            var victim = entity as BasePlayer;
            if (victim == null || info == null || info.InitiatorPlayer == null) return;

            var killer = info.InitiatorPlayer;
            if (killer == victim || killer.IsNpc || killer.IsDead() || !killer.IsConnected) return;

            if (config.PermissionOnly && !permission.UserHasPermission(killer.UserIDString, PermEnabled)) return;

            var itemDefinition = ItemManager.FindItemDefinition(config.Shortname);
            if (itemDefinition == null)
            {
                if (!shortnameWarningSent)
                {
                    shortnameWarningSent = true;
                    PrintWarning(Msg("InvalidItem"));
                }
                return;
            }

            var item = ItemManager.CreateByItemID(itemDefinition.itemid, Math.Max(1, config.Amount));
            if (item == null) return;

            killer.GiveItem(item);
            killer.ChatMessage(Msg("Reward", killer.UserIDString, item.amount, item.info.displayName.english, victim.displayName));
        }
    }
}