error indexing must appear last

I have a code which tracks a series of footballs in a video.

I have found the coordinates for the balls in the video, and now I am trying to crop each of the larger images using the x and y coordinates of the balls.

However when I run the code to sub-image this, I get the error that indexing must appear last in an indexing expression. Can anybody help me solve this?

% Identify and track the particles for frames 1 and 2
for k = 1:numFrames; 
    %binarize frames 1 and 2 from the video (using rgb2gray)
    frame_1 = rgb2gray(read(obj,k+start_frame-1));
    frame_2 = rgb2gray(read(obj,k+start_frame));
    %identify the circles in frames 1 and 2 with radii between the defined min and max
    circles_1 =imfindcircles(frame_1,[min_radius,max_radius],'Sensitivity',quality,'Method','TwoStage');
    circles_2 =imfindcircles(frame_2,[min_radius,max_radius],'Sensitivity',quality,'Method','TwoStage'); %returns the indicies of the closest points in the 2 vectors
    % identifies where each circle has moved between frames 1 and 2 
    [index,dist] = dsearchn(circles_2,circles_1);
    % here we have the distances not in order 
    % assign the circles from frames 1 and 2 to x and y coordinate variables
    x_1{k} = circles_1(:,1);
    x_2{k} = circles_2(index,1);
    y_1{k} = circles_1(:,2);
    y_2{k} = circles_2(index,2);
end

%% Crop frames 1 and 2 into sub-images from the coordinates of the circles 
r = 10;
for k = 1:numFrames
%subimage the balls in frames 1 and 2 by shrinking them to the coordinates of the balls
subframe1 = frame_1(round(y_1)-r:round(y_1)+r)(round(x_1)-r:round(x_1)+r);
subframe2 = frame_2(round(y_2)-r:round(y_2)+r,round(x_2)-r:round(x_2)+r);
end 

Error: ()-indexing must appear last in an index expression.
 

[Walter Roberson]

subframe1 = frame_1(round(y_1)-r:round(y_1)+r, round(x_1)-r:round(x_1)+r);

[C.G.]

Great, thank you that has worked.