...

if(plugin.speedArcher.contains(p.getName())) {
                        PotionEffectType pet = PotionEffectType.SPEED;
                        final PotionEffect effect = pet.createEffect(100, 0);
                        p.addPotionEffect(effect, true);
                        plugin.getServer().getScheduler().runTaskTimer(plugin, new Runnable() {
                            @Override
                            public void run() {
                                p.addPotionEffect(effect, true);
                            }
                        }, 20L, 20L);
                    }