If you've had a problem with server crashes on startup, here are some steps you can take to isolate the problem and figure out what's causing the crash.
1. Get a new Spigot build.
This can often fix the problem. Play around with the different builds and see if a newer/older build makes it work. Didn't work? Step 2.
2. Run without worlds.
Before messing with your plugins, corrupted worlds can often cause startup crashes. Try running your server without your worlds and see if that fixes the problem. You do this by taking your world(s) out of your server directory. If it does work, one of your worlds may be corrupted. Isolate the problematic world by starting the server with only one world loaded at a time. If you can delete it, do it. If not, run a chunk fixing tool. No success? Step 3.
3. Run without plugins.
Download the whole server, and try deleting/renaming the plugins folder before startup. If the error is gone, you know it's a plugin causing the problem. Is it a plugin? Step 3a.
3a. Update all plugins.
It may seem like a lot of work, but it's good to have all your plugins up-to-date. Error persists? Step 3b.
3b. Check individual plugins.
Now that you know it's a plugin causing the problem, it's time to comb through your plugin list and find the problematic plugin. Start out with only half your plugins loaded (put the other half somewhere else). If the problem is gone, you know it was one of the plugins you put aside. If the problem is still there, you know it's a plugin you left in your plugins folder. Keep halving the plugins until you've narrowed it down to a single plugin. Confirm that it's causing the problem.
If all else fails, post your crash in the Bugs section of the Spigot forums. Be sure to use pastebin.com for all your console errors, and make sure to give as much detail as possible.