Do you have a dog? this sounds typically of urine burn. If no dog then it could be due to a fungal infection. Not sure what you could do about it though.

A photo of the problem would be good for diagnostic purposes

If you don't have a dog - could be the local fox!

I read about this problem a few days ago but can't find the article now.

It's fusarium which causes orange-brown patches, 1-2 inches across, which increase in size under suitable conditions and join up to form large areas. Often active after snow cover when it appears as a brown ring around a straw-coloured or pinkish centre. It can occur at any time of year, most types of soil. Annual meadowgrass particularly susceptible. Your local Garden Centre should be able to advise you on treatments

In the papers yesterday it talked of snow fungus being seen on many lawns after the snow this year it said no treatment was need as it would also go away in a few weeks