That looks like very small pot, especially for indeterminate tomato plant. And mulching with grass clippings isn't such great idea in container - will not help with fruit production. Too much nitrogen will support lots of growth but not flowering. Not sure why it's not flowering if in enough sun, it also looks quite 'skinny'. Did you remove side shoots? - doesn't look like it, but can't tell for sure looking at the photo. What fertilizer did you use? - maybe get one for tomato plants? I fertilize with MG 24-8-16 if I water; it has been raining a lot :). I have a "leftover" plant in a very small, 4" pot (!!! - do not have room for any more...) and it actually has few tomatoes, poor pant.

That is way too small a container for Sungolds!! I grow mine in a 20G black nursery pot. Your plant is completely root bound and is not getting the nutrients it needs.

I would try very carefully to repot in a much larger container but if you feel that not possible, then you should be fertilizing with every watering with a dilute solution of whatever liquid or water soluble fertilizer you are using. 1/4 strength is fine but consistently, not once and awhile.

The pot is too small - the plant is potbound.

I made that mistake many years ago as a newbie gardener - I put everything in pots that were way too small. LOL! A few years ago I had an extra cherry tomato and put it in a 5 gal pot and it did terribly compared to the ones in the ground. They need a lot of room.

Thanks everyone---do you think there is a chance the plant could be saved if I transplanted it to a bigger container or is it too late?

No it's not too late. There is enough growing season left and tomatoes are pretty robust plants, they grow like weeds for me. Put it in a larger container or in the ground.

If using a pot I would use at least a 10 gal pot, although a 20g as Gardengal mentioned would be ideal.

Allison

I asked if you are pinching off side shoots...???

Thanks everyone! No, I haven't been pinching off the suckers since it wasn't growing very well...my tomatoes in the raised bed grew like weeds!

You'll help plant growing better if you do - having just 1 stem rather than many to put all the energy in. And it is much easier to manage. I usually leave just one or maybe 2 stems, when plant gets bigger. It needs bigger and stronger support stake too. And I cut off the top growing tips once it gets too tall (7-8') - don't need to climb up the ladder to pick off tomatoes :) But they are your plants, so do as you like - for example, if you want lots of branches, or super tall plant...