Nade Training v1.0.4-beta by roge. Add file to "Counter-Strike Global Offensive/csgo/scripts/vscripts" then run `script_execute NT.nut` to run.

NT.nut

const NT_TIMER_ENTITY_TARGET_NAME = "NT_TimerEnt";
const NT_SCRIPT_VERSION = "1.0.4-beta";

NT_LastGrenade <- null;
NT_LastRestoredGrenade <- null;
NT_SavedGrenadePosition <- null;
NT_SavedGrenadeVelocity <- null;
NT_AwaitingSave <- false;
NT_IsPaused <- false;

function NT_Setup() {
    printl("Setting up Nade Training..."); 
    
    /* Destroy old timer entities. */
    local entity = null;
    while(entity = Entities.FindByName(entity, NT_TIMER_ENTITY_TARGET_NAME)) {
        entity.Destroy();
    }

    /* Create new timer entity. */
    local timerEnt = Entities.CreateByClassname("logic_timer");
    EntFireByHandle(timerEnt, "disable", "", 0.0, null, null);
    timerEnt.__KeyValueFromString("targetname", NT_TIMER_ENTITY_TARGET_NAME);
    timerEnt.__KeyValueFromFloat("refiretime", 0.02);
    timerEnt.__KeyValueFromInt("startdisabled", 0);
    timerEnt.__KeyValueFromInt("UseRandomTime", 0);
    timerEnt.ConnectOutput("ontimer", "NT_Think");
    EntFireByHandle(timerEnt, "enable", "", 0.0, null, null);
    
    /* Create aliases to script functions. This is a hacky way of registering commands */
    SendToConsole("alias nt_save \"script NT_PromptSave()\"");
    SendToConsole("alias nt_pause \"script NT_TogglePause()\"");
    
    NT_DualPrintFormatted("Nade Training v" + NT_SCRIPT_VERSION + " loaded!");
    NT_DualPrintFormatted("Rewritten by roge <roge@riseup.net>");
    NT_DualPrintFormatted("Originally written by S0lll0s, Bidj, and Rurre");
    NT_DualPrintFormatted("Use console command `nt_save` to save next grenade.");
    NT_DualPrintFormatted("Use console command `nt_pause` to toggle the plugin.");
}

function NT_IsRunning() {
    return Entities.FindByName(null, NT_TIMER_ENTITY_TARGET_NAME) != null;
}

function NT_TogglePause() {
    if(!NT_IsRunning()) return;
    NT_IsPaused = !NT_IsPaused;
    NT_DualPrintFormatted(NT_IsPaused ? "Script is paused. Grenades can now be thrown freely." : "Script is no longer paused. Grenades will be saved and restored.");
    NT_AwaitingSave = false;
}

function NT_PromptSave() {
    if(!NT_IsRunning()) return;
    if(NT_IsPaused) {
        NT_DualPrintFormatted("Grenades cannot be saved while script is paused.");
        return;
    }
    
    NT_AwaitingSave = true;
    NT_DualPrintFormatted("Next Flashbang or HE Grenade will be saved.");
}

function NT_DualPrintFormatted(str) {
    printl("[Nade Training] " + str);
    ScriptPrintMessageChatAll("\x01[\x0BNade Training\x01] " + str);
}

function NT_Think() {
    if(NT_IsPaused) return;

    NT_HandleGrenadeClass("flashbang_projectile");
    NT_HandleGrenadeClass("hegrenade_projectile");
}

function NT_HandleGrenadeClass(classname) {
    local grenade = null;
    while(grenade = Entities.FindByClassname(grenade, classname)) {
        if(grenade == NT_LastGrenade) continue;
        
        if(NT_AwaitingSave)
            NT_SaveGrenade(grenade);
        else
            NT_RestoreGrenade(grenade);
            
        NT_LastGrenade = grenade;
    }
}

function NT_SaveGrenade(grenade) {
    if(NT_LastRestoredGrenade != null && grenade == NT_LastRestoredGrenade) {
        NT_DualPrintFormatted("Please wait for all existing grenades to detonate before saving.");
        NT_DualPrintFormatted("Nothing saved.");
        NT_PromptSave();
        return;
    }
    NT_SavedGrenadePosition = grenade.GetCenter();
    NT_SavedGrenadeVelocity = grenade.GetVelocity();
    NT_DualPrintFormatted("Grenade saved.");
    NT_AwaitingSave = false;
}

function NT_RestoreGrenade(grenade) {
    if(NT_SavedGrenadePosition == null || NT_SavedGrenadeVelocity == null) return;
    grenade.SetAbsOrigin(NT_SavedGrenadePosition);
    grenade.SetVelocity(NT_SavedGrenadeVelocity);
    NT_LastRestoredGrenade = grenade;
}

NT_Setup();