Stutter and frame drops come from three places: the phone running out of headroom, the phone throttling because of heat, or the game asking for more than the hardware can deliver. Optimizing means reducing load on all three fronts rather than hunting for a single magic setting.
Close background apps, restart the device so memory is genuinely freed, and keep several gigabytes of storage available. Turn off battery saver while playing, since it deliberately limits processor speed. On Android, allowing the game unrestricted background activity prevents the system from throttling it mid-match. These steps cost nothing and often produce the largest gain.
Resolution and shadows are usually the most expensive options, followed by anti-aliasing and particle effects. Lower those first and keep textures if memory allows. Locking the frame rate at a level the phone can hold consistently feels smoother than an unlocked rate that swings between high and low, because consistency is what the eye reads as smooth.
Sustained heat forces the system to throttle, which shows up as frames that were fine for ten minutes and then are not. Remove thick cases, avoid playing while fast charging, and take short breaks. If the stutter only appears in online matches while single-player is smooth, the problem is the connection, not the hardware, so troubleshoot Wi-Fi and server region instead.
Do cleaner or booster apps really improve FPS?
Rarely. Closing apps and restarting achieves the same thing, while booster apps run in the background themselves and often request broad permissions.
Why is my game smooth at first then stutters?
That is the classic sign of thermal throttling. Let the phone cool, remove the case, lower graphics settings, and cap the frame rate for a steadier result.