Next command in command block orconsole:
/summon Fireball ~ ~3 ~

cause game to crash

Report:

---- Minecraft Crash Report ----
// Ooh. Shiny.

Time: 11.10.13 3:49
Description: Unexpected error

java.lang.NullPointerException
at bkv.a(SourceFile:303)
at bkv.a(SourceFile:900)
at bkv.b(SourceFile:814)
at ays.ab(SourceFile:783)
at ays.e(SourceFile:706)
at net.minecraft.client.main.Main.main(SourceFile:103)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

– Head –
Stacktrace:
at bkv.a(SourceFile:303)
at bkv.a(SourceFile:900)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [bip['Player'/9, l='MpServer', x=7,86, y=34,62, z=-819,14]]
Chunk stats: MultiplayerChunkCache: 225, 225
Level seed: 0
Level generator: ID 01 - flat, ver 0. Features enabled: false
Level generator options:
Level spawn location: World: (4,4,-838), Chunk: (at 4,0,10 in 0,-53; contains blocks 0,0,-848 to 15,255,-833), Region: (0,-2; contains chunks 0,-64 to 31,-33, blocks 0,0,-1024 to 511,255,-513)
Level time: 90619 game time, 4393 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
Forced entities: 9 total; [vx['entity.MinecartHopper.name'/1, l='MpServer', x=-14,53, y=35,50, z=-841,50], vx['entity.MinecartHopper.name'/2, l='MpServer', x=9,50, y=33,50, z=-851,88], uu['Mr. Pig'/3, l='MpServer', x=11,47, y=34,00, z=-852,31], vx['entity.MinecartHopper.name'/4, l='MpServer', x=8,50, y=33,50, z=-844,50], vx['entity.MinecartHopper.name'/5, l='MpServer', x=8,50, y=33,50, z=-843,50], vx['entity.MinecartHopper.name'/6, l='MpServer', x=8,50, y=33,50, z=-842,53], xm['Fireball'/1523, l='MpServer', x=10,18, y=33,79, z=-816,50], vx['entity.MinecartHopper.name'/7, l='MpServer', x=3,50, y=36,50, z=-840,50], bip['Player'/9, l='MpServer', x=7,86, y=34,62, z=-819,14]]
Retry entities: 0 total; []
Server brand: vanilla
Server type: Integrated singleplayer server
Stacktrace:
at bik.a(SourceFile:302)
at ays.b(SourceFile:1924)
at ays.e(SourceFile:720)
at net.minecraft.client.main.Main.main(SourceFile:103)

– System Details –
Details:
Minecraft Version: 13w41a
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.7.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 264243424 bytes (252 MB) / 550371328 bytes (524 MB) up to 1908932608 bytes (1820 MB)
JVM Flags: 1 total; -Xmx2G
AABB Pool Size: 18003 (1008168 bytes; 0 MB) allocated, 50 (2800 bytes; 0 MB) used
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Launched Version: 13w41a
LWJGL: 2.9.0
OpenGL: GeForce GTX 660/PCIe/SSE2 GL version 4.3.0, NVIDIA Corporation
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Packs: []
Current Language: English (US)
Profiler Position: N/A (disabled)
Vec3 Pool Size: 207 (11592 bytes; 0 MB) allocated, 61 (3416 bytes; 0 MB) used