why did heck Tate and the other men come to see Atticus ?

Heck Tate went to tell Atticus that Tom Robinson was being transferred. The other men congregated in Atticus' front yard to show their support for him. 

The visit that Heck Tate and the men had paid to Atticus was uncalled for. The reason that they visited him was to warn him. They car for Atticus and think that by defending Tom Robinson he will be harmed or affected. They also came to warn him that there may be some trouble with the Old Sarum bunch. They are planning to lynch Tom Robinson.